Fix boinc platform strings for Android

[truboxl]

Description of the Change
Some compiled clients may appear as $ARCH-unknown-linux-android instead of
$ARCH-android-linux-gnu to project servers
This is because of Android NDK specifies $ARCH-linux-android triplets and
users forget to specify --with-boinc-platform

Fix this in boinc_platform.m4 so that Android boinc platform strings changes are not needed across all projects

boinc_alt_platform is excluded to prepare for 64bit only Android devices
Users can add back requesting 32bit tasks with --with-boinc-alt-platform during compile or <alt_platform> during runtime

Alternate Designs
Feedbacks are welcome.

Release Notes
N/A

[codecov]

Codecov Report

Merging #3740 into master will increase coverage by 0.82%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #3740      +/-   ##
==========================================
+ Coverage   15.66%   16.49%   +0.82%     
==========================================
  Files         136      133       -3     
  Lines       13873    13171     -702     
  Branches     1770     1630     -140     
==========================================
- Hits         2173     2172       -1     
+ Misses      11568    10867     -701     
  Partials      132      132              

Impacted Files	Coverage Δ
lib/url.cpp	92.90% <0.00%> (-7.10%)	⬇️
...c/main/java/edu/berkeley/boinc/utils/BOINCUtils.kt	23.80% <0.00%> (-0.52%)	⬇️
...rc/main/java/edu/berkeley/boinc/rpc/RpcClient.java	29.38% <0.00%> (-0.11%)	⬇️
lib/util.cpp	0.00% <0.00%> (ø)
lib/mfile.cpp	0.00% <0.00%> (ø)
lib/parse.cpp	11.29% <0.00%> (ø)
lib/coproc.cpp	0.00% <0.00%> (ø)
lib/filesys.cpp	0.00% <0.00%> (ø)
lib/miofile.cpp	0.00% <0.00%> (ø)
lib/md5_file.cpp	0.00% <0.00%> (ø)
... and 39 more

[AenBleidd]

I'm not sure whether these lines are correct or not.
@davidpanderson, could you please take a look at it?
Thanks in advance

[davidpanderson]

The official list of platform names is here:
https://boinc.berkeley.edu/trac/wiki/BoincPlatforms
These are all consistent with that.

[AenBleidd]

@truboxl, could you please add similar logic to define boinc_alt_platform?

[truboxl]

I think the intention is not to add them to prepare for 64bit only systems. If the devs think it should be included then ok I guess I will add them, Once these added I think can remove --with-boinc-platform and etc from build scripts...

[AenBleidd]

You still need them in build scripts when cross-compiling for different platforms but if you build it for your native platform - then yes, no need to specify this parameter in build script

[truboxl]

Ah yes you are right
I totally forgot needing to pass --host=$ARCH-linux-android
using that will automatically picks up the respective platform strings without needing overrides --with-boinc-platform and etc

This is inline with https://developer.android.com/ndk/guides/standalone_toolchain#projects_using_autoconf and https://github.com/curl/curl/blob/master/docs/INSTALL.md#android