[sdks] runtime doesn't link with Xcode 11.4 due to weak import symbol ___darwin_check_fd_set_overflow #19393
Description
How to reproduce:
$ git clone mono && cd mono
$ git submodule update --init --recursive
$ xcodebuild -version
Xcode 11.4
Build version 11E146
$ XCODE_DIR=`xcode-select -p` ENABLE_IOS=1 make -C sdks/builds -j build-ios-target64
[...]
CCLD libmonosgen-2.0.la
ld: warning: -undefined dynamic_lookup is deprecated on iOS
ld: weak import of symbol '___darwin_check_fd_set_overflow' not supported because of option: -no_weak_imports for architecture arm64
clang: error: linker command failed with exit code 1 (use -v to see invocation)
make[6]: *** [libmonosgen-2.0.la] Error 1This breaks the Xamarin.iOS build when building with MONO_BUILD_FROM_SOURCE=1 set (which is only a developer option, but eventually we will have to deal with it).
Unity hits a similar issue on macOS: https://forum.unity.com/threads/empty-project-fails-to-compile-using-il2cpp-unity-2019-3-7-case-1231096.854743/ and https://forum.unity.com/threads/il2cpp-macstandalone-and-xcode-11-4.855187/
The suggested solution is to update macOS to at least 10.15.4, but that doesn't help for the iOS case.
Also I tried to bump the iOS min version to 13.4 (which needs some tiny fix around logging; just take the implementation for watchOS in the same file):
Line 26 in a17ab75
It doesn't help either (and anyway we could only go as far as 10.3 due to iOS/armv7).
Not sure what to do about it.