Multi platform monodroid BCL builds

[lambdageek]

Now that mscorlib and System depend on System.Native on non-windows platform, our BCL is no longer portable across platforms - a BCL built for macOS cannot simply be copied across to a Windows machine and expected to run. The interop code in a windows-specific build will directly P/Invoke into the Win32 APIs, whereas the interop code on other platforms delegates to System.Native which has internal calls to a platform specific native library libmono-native.{so,dylib}. Moreover it is merely a matter of coincidence that, for example, Android and macOS have the same symbols with the same semantics in their libmono-native - they could potentially diverge to take advantage of platform-specific capabilities.

Products such as Android Designer on Windows have the goal of running "the true monodroid BCL" profile. Currently they achieve that by copying the monodroid-targeted-at-Android BCL to Windows and running a host Mono runtime there. For reasons outlined above, this will no longer work.

Tasks:

DONE: Phase 1 - win32

• [x] monodroid on win32 profile - for Android Designer on Windows.
  • [x] master (and 2019-06 onward) -> #14424
  • [x] 2019-02 backport -> #14504
• [x] Make the Android SDK code build monodroid on win32 on Windows.
  • [x] master (and 2019-06 onward) -> #14402
  • [x] 2019-02 backport -> #14472
• [x] Publish android archive from Jenkins pipeline (update scripts/ci/pipeline/sdks-archive.groovy to publish results at https://jenkins.mono-project.com/job/archive-mono/ )
  • [x] 2019-02 -> #14503, #14519 and #14516
  • [x] master (and 2019-06 onward) -> #14699
• [x] CI
  • [x] master monodroid-win32 on Windows - https://jenkins.mono-project.com/job/za/
  • [x] PR - https://jenkins.mono-project.com/view/Pull%20requests/job/xa/ (rebuild with @monojenkins build Windows x64 Android SDK)

Next: Phase 2 - CI and testing

• [x] CI: Make "Windows x64 Android SDK" PR lane required - https://jenkins.mono-project.com/view/Pull%20requests/job/xa/
• [ ] Make tests pass on win32 when running on the win32 monodroid BCL
  • [ ] Add to CI

Future

• BCL
  • [ ] monodroid on macos profile - for Designer on Mac (today the monodroid on Android profile is close enough that it accidentally works)
  • [ ] monodroid on Linux profile (for CI; this is substantially the same as Android, probably)
  • [ ] Publish the monodroid on macos Android SDK archive (needs sdks/ and groovy changes)
  • [ ] CI: Setup PR lane that builds monodroid on macos Android SDK.
• Windows SDK archive
  • [ ] Build Windows host mono binaries on win32 using MSVC and include in the win32 archive instead of using MXE on macOS.
  • [ ] Build Windows AOT cross compilers on win32 using MSVC (needs runtime work) instead of using MXE on macOS.

[lambdageek]

What I've learned today: if you build mono with --enable-monodrdoid it takes a hard dependency on zlib. As far as I can tell it only works with an external zlib (at least the way that sdks/builds/android.mk is set up).

It's not a problem right now, because for just the BCL build we don't need to compile with --enable-monodroid (which controls the runtime's support for XA; --with-monodroid or explicitly building the BCL with build_profiles='monodroid' is what builds the BCL), but if we start doing host builds on Windows, we will need to install mingw64-x86_64-zlib on Cygwin on CI.