Add ARMv8-M and ARMv8.1-M support for Darwin#12844

DougGregor wants to merge 2 commits intoswiftlang:stable/21.xswiftlang/llvm-project:stable/21.xfrom

DougGregor:armv8m-stable-21DougGregor/llvm-project:armv8m-stable-21Copy head branch name to clipboard