llvm@7: backport fixes from llvm@12, and prepare for upstreaming
llvm@7: backport fixes from llvm@12, and prepare for upstreaming

Closes #23522.

Signed-off-by: Daniel Nachun <67d4b1adb270d50ecb7ec053ff144a69f3054d28@users.noreply.github.com>

Linuxbrew/homebrew-core,Linuxbrew/homebrew-core