autotools: fix/improve gcc and Apple clang version detection

[vszakats]

• Before this patch we expected n.n -dumpversion output, but Ubuntu
  may return n-win32 (also with -dumpfullversion). Causing these
  errors and failing to enable picky warnings:

  ../configure: line 23845: test: : integer expression expected
  

  Ref: https://github.com/libssh2/libssh2/actions/runs/6263453828/job/17007893718#step:5:143

  Fix that by stripping any dash-suffix and handling a dotless (major-only)
  version number by assuming .0 in that case.

  9.3-posix, 9.3-win32, 6, 9.3.0, 11, 11.2, 11.2.0
  Ref: fix version detection in str_to_version for versions formatted as (n).(n)-suffix mamedev/mame#9767

• fix Apple clang version detection for releases between
  'Apple LLVM version 7.3.0' and 'Apple LLVM version 10.0.1' where the
  version was under-detected as 3.7 llvm/clang equivalent.

• fix Apple clang version detection for 'Apple clang version 11.0.0'
  and newer where the Apple clang version was detected, instead of its
  llvm/clang equivalent.

• display detected clang/gcc/icc compiler version.

Via libssh2:

• libssh2/libssh2@00a3b88
  autotools: fix selecting wincng in cross-builds libssh2/libssh2#1187
• libssh2/libssh2@89ccc83
  autotools: fix dotless gcc and Apple clang version detections libssh2/libssh2#1232

Closes #12362

[bagder]

gcc version detection is still half broken because we translate '10' to '10.10' because cut -d. -f2 returns the first word if the delimiter missing.

Is cut's -s portable enough to be used in the -f2 invocation ? "do not print lines not containing delimiters"

[vszakats]

-s is there on macOS and GNU, and part of POSIX.2: https://pubs.opengroup.org/onlinepubs/9699919799/utilities/cut.html

But, we need to fill the blank with a zero, so this is what I was experiment with instead:

--- a/m4/curl-compilers.m4
+++ b/m4/curl-compilers.m4
@@ -160,7 +160,11 @@ AC_DEFUN([CURL_CHECK_COMPILER_GNU_C], [
     compiler_id="GNU_C"
     gccver=`$CC -dumpversion`
     gccvhi=`echo $gccver | cut -d . -f1`
-    gccvlo=`echo $gccver | cut -d . -f2`
+    if echo $gccver | grep -F "." >/dev/null; then
+      gccvlo=`echo $gccver | cut -d . -f2`
+    else
+      gccvlo="0"
+    fi
     compiler_num=`(expr $gccvhi "*" 100 + $gccvlo) 2>/dev/null`
     flags_dbg_yes="-g"
     flags_opt_all="-O -O0 -O1 -O2 -O3 -Os -Og -Ofast"

[vszakats]

Merged #12358 into this PR, and also applied the Xcode version fixes from libssh2/libssh2#1232.