[compiler-rt][Darwin] Add arm64 to simulator platforms

[thieta]

Summary

I was looking around and noticed that builtins for iossim, tvossim
and watchossim was missing arm64 builds, while apple's clang
toolchain ship with these. After a bit of searching around it just
seems like these are not listed correctly in CMake to be enabled.

I enabled just arm64 since I saw that Apple clang didn't include
arm64e.

[t.p.northover]

Looks like it matches what we build with Xcode so I think this is OK. I dread to think what Xcode does for watchossim does though, that should totally be arm64_32, but it's not.

[mstorsjo]

In D118759#3289574, @t.p.northover wrote:

I dread to think what Xcode does for watchossim does though, that should totally be arm64_32, but it's not.

Isn't the simulator environment just plain arm64 even for watchos? On the line above (line 126) there's already arm64_32 in DARWIN_watchos_BUILTIN_ALL_POSSIBLE_ARCHS.

[t.p.northover]

I'm afraid I've had to revert this (with becb29aeb6a2) because it was causing CI failures: https://green.lab.llvm.org/green/job/clang-stage1-cmake-RA-expensive/21780/console. It looks like older Xcodes didn't allow arm64 builds in the simulator SDK (because M1 Macs were secret at the time I assume). It might be possible to add logic to detect this, I'll see what we've got internally.

[thieta]

In D118759#3292922, @t.p.northover wrote:

I'm afraid I've had to revert this (with becb29aeb6a2) because it was causing CI failures: https://green.lab.llvm.org/green/job/clang-stage1-cmake-RA-expensive/21780/console. It looks like older Xcodes didn't allow arm64 builds in the simulator SDK (because M1 Macs were secret at the time I assume). It might be possible to add logic to detect this, I'll see what we've got internally.

That's unfortunate - but not unexpected. Let me know if there is anything I can help with. This should also be reverted from the 14.x branch then @tstellar - since it causes issues with older Xcodes.

compiler-rt/cmake/builtin-config-ix.cmake

if(APPLE)
 
   if(COMPILER_RT_ENABLE_IOS)
     list(APPEND DARWIN_EMBEDDED_PLATFORMS ios)
     set(DARWIN_ios_MIN_VER_FLAG -miphoneos-version-min)
     set(DARWIN_ios_BUILTIN_MIN_VER 6.0)
     set(DARWIN_ios_BUILTIN_MIN_VER_FLAG
       ${DARWIN_ios_MIN_VER_FLAG}=${DARWIN_ios_BUILTIN_MIN_VER})
     set(DARWIN_ios_BUILTIN_ALL_POSSIBLE_ARCHS ${ARM64} ${ARM32})
-    set(DARWIN_iossim_BUILTIN_ALL_POSSIBLE_ARCHS ${X86} ${X86_64})
+    set(DARWIN_iossim_BUILTIN_ALL_POSSIBLE_ARCHS ${X86} ${X86_64} arm64)
   endif()
   if(COMPILER_RT_ENABLE_WATCHOS)
     list(APPEND DARWIN_EMBEDDED_PLATFORMS watchos)
     set(DARWIN_watchos_MIN_VER_FLAG -mwatchos-version-min)
     set(DARWIN_watchos_BUILTIN_MIN_VER 2.0)
     set(DARWIN_watchos_BUILTIN_MIN_VER_FLAG
       ${DARWIN_watchos_MIN_VER_FLAG}=${DARWIN_watchos_BUILTIN_MIN_VER})
     set(DARWIN_watchos_BUILTIN_ALL_POSSIBLE_ARCHS armv7 armv7k arm64_32)
-    set(DARWIN_watchossim_BUILTIN_ALL_POSSIBLE_ARCHS ${X86})
+    set(DARWIN_watchossim_BUILTIN_ALL_POSSIBLE_ARCHS ${X86} arm64)
   endif()
   if(COMPILER_RT_ENABLE_TVOS)
     list(APPEND DARWIN_EMBEDDED_PLATFORMS tvos)
     set(DARWIN_tvos_MIN_VER_FLAG -mtvos-version-min)
     set(DARWIN_tvos_BUILTIN_MIN_VER 9.0)
     set(DARWIN_tvos_BUILTIN_MIN_VER_FLAG
       ${DARWIN_tvos_MIN_VER_FLAG}=${DARWIN_tvos_BUILTIN_MIN_VER})
     set(DARWIN_tvos_BUILTIN_ALL_POSSIBLE_ARCHS armv7 arm64)
-    set(DARWIN_tvossim_BUILTIN_ALL_POSSIBLE_ARCHS ${X86} ${X86_64})
+    set(DARWIN_tvossim_BUILTIN_ALL_POSSIBLE_ARCHS ${X86} ${X86_64} arm64)
   endif()
 
   set(BUILTIN_SUPPORTED_OS osx)
 
   # We're setting the flag manually for each target OS
   set(CMAKE_OSX_DEPLOYMENT_TARGET "")
 
   # NOTE: We deliberately avoid using `DARWIN_<os>_ARCHS` here because that is