config/zfs-build.m4: add --with-vendor flag

[gyakovlev]

Motivation and Context

This will allow to override autodetection of distribution, which
is based on checking presense of /etc/*-release files.

Build systems makes a lot of file location assumptions based on
detected distribution.

Some distributions (like gentoo) may prefer explicitly
setting --with-vendor=gentoo to avoid autodetection.

Since autodetection checks all files in order, current script may
misdetect even on gentoo system if /etc/redhat-release file is present

Default behavior is unchanged and default is --with-vendor=check

Description

here's resulting ./configure snippet this change generates

# Check whether --with-vendor was given.                                                                                                                                                                           
if test "${with_vendor+set}" = set; then :                                                                                                                                                                         
  withval=$with_vendor; with_vendor=$withval                                                                                                                                                                       
else                                                                                                                                                                                                               
  with_vendor=check                                                                                                                                                                                                
fi                                                                                                                                                                                                                                                                                                                                                                                                                       
        if test "x$with_vendor" = "xcheck"; then :                                                                                                                                                                 
                                                                                                                                                                                                                   
                if test -f /etc/toss-release ; then                                                                                                                                                                
                        VENDOR=toss ;                                                                                                                                                                              
                elif test -f /etc/fedora-release ; then                                                                                                                                                            
                        VENDOR=fedora ;                                                                                                                                                                            
                elif test -f /etc/redhat-release ; then                                                                                                                                                            
                        VENDOR=redhat ;                                                                                                                                                                            
                elif test -f /etc/gentoo-release ; then                                                                                                                                                            
                        VENDOR=gentoo ;                                                                                                                                                                            
                elif test -f /etc/arch-release ; then                                                                                                                                                              
                        VENDOR=arch ;                                                                                                                                                                              
                elif test -f /etc/SuSE-release ; then                                                                                                                                                              
                        VENDOR=sles ;                                                                                                                                                                              
                elif test -f /etc/slackware-version ; then                                                                                                                                                         
                        VENDOR=slackware ;                                                                                                                                                                         
                elif test -f /etc/lunar.release ; then                                                                                                                                                             
                        VENDOR=lunar ;                                                                                                                                                                             
                elif test -f /etc/lsb-release ; then                                                                                                                                                               
                        VENDOR=ubuntu ;                                                                                                                                                                            
                elif test -f /etc/debian_version ; then                                                                                                                                                            
                        VENDOR=debian ;                                                                                                                                                                            
                elif test -f /etc/alpine-release ; then                                                                                                                                                            
                        VENDOR=alpine ;                                                                                                                                                                            
                elif test -f /bin/freebsd-version ; then                                                                                                                                                           
                        VENDOR=freebsd ;                                                                                                                                                                           
                else                                                                                                                                                                                               
                        VENDOR= ;                                                                                                                                                                                  
                fi                                                                                                                                                                                                 
elif  test "x${with_vendor}" != x; then :                                                                                                                                                                                                                                                                                                                                                               
                        VENDOR="$with_vendor"                                                                                                                                                                      
else                                                                                                                                                                                                               
   VENDOR= ;                                                                                                                                                                                                       
                                                                                                                                                                                                                   
                                                                                                                                                                                                                   
fi 

How Has This Been Tested?

built with --with-config=user --with-vendor=VAL passing different VAL, both autodetection and explicit value work fine. Empty or undefined values handled as well.

formatting may need some work.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Performance enhancement (non-breaking change which improves efficiency)
• Code cleanup (non-breaking change which makes code smaller or more readable)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation (a change to man pages or other documentation)

Checklist:

• My code follows the ZFS on Linux code style requirements.
• I have updated the documentation accordingly.
• I have read the contributing document.
• I have added tests to cover my changes.
• I have run the ZFS Test Suite with this change applied.
• All commit messages are properly formatted and contain Signed-off-by.

[gyakovlev]

just to clarify, we had couple of users who had both /etc/gentoo-release and /etc/redhat-release files present, redhat file was installed to satisfy some kind of closed-source software which expects this file. and as a side-effect it broke zfs builds, because files were placed into wrong directories (/etc/sysconfig instead of /etc/conf.d).

[codecov]

Codecov Report

Merging #10835 into master will increase coverage by 0.03%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master   #10835      +/-   ##
==========================================
+ Coverage   79.64%   79.67%   +0.03%     
==========================================
  Files         395      395              
  Lines      125066   125066              
==========================================
+ Hits        99609    99649      +40     
+ Misses      25457    25417      -40     

Flag	Coverage Δ
#kernel	80.44% <ø> (+0.04%)	⬆️
#user	65.64% <ø> (+0.90%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
cmd/zdb/zdb_il.c	30.86% <0.00%> (-24.08%)	⬇️
cmd/zvol_id/zvol_id_main.c	76.31% <0.00%> (-5.27%)	⬇️
module/zstd/zfs_zstd.c	80.74% <0.00%> (-4.28%)	⬇️
module/zfs/vdev_raidz.c	89.11% <0.00%> (-4.25%)	⬇️
lib/libzfs/libzfs_changelist.c	85.01% <0.00%> (-1.13%)	⬇️
module/os/linux/zfs/vdev_disk.c	78.85% <0.00%> (-1.08%)	⬇️
module/zcommon/zfs_uio.c	87.75% <0.00%> (-1.03%)	⬇️
module/zfs/zio.c	87.50% <0.00%> (-0.97%)	⬇️
module/zfs/ddt.c	87.81% <0.00%> (-0.78%)	⬇️
module/icp/api/kcf_mac.c	38.28% <0.00%> (-0.58%)	⬇️
... and 56 more

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