The aarch64 task was already a cross build on the Intel b-osx-1015 workers, so neither build executes what it
compiles. build.py's --osx_arch only acts on a macOS host, so the Darwin cmake variables are passed directly,
the way build-llvm-common.sh does for compiler-rt, with linux64-clang-toolchain replacing the Mach-O
macosx64-clang and the mac cmake/ninja fetches. Deployment targets are set explicitly to Firefox's (10.15
x86_64, 11.0 arm64).
-fuse-ld=lld goes in the compile flags because cmake's try_compile checks, including the one behind
--enable_lto, don't inherit CMAKE_*_LINKER_FLAGS and would silently disable LTO. CMAKE_ASM_COMPILER_TARGET is
needed or the .S files are assembled for the host.
Differential Revision: https://phabricator.services.mozilla.com/D325157
Ryan VanderMeulen
1dfefda069