Fix what seems to be a mismerge of a couple patches relating to StackFrameLists…#11712

JDevlieghere merged 3 commits intoswiftlang:stable/21.xswiftlang/llvm-project:stable/21.xfrom

jimingham:fixup-stack-writer-mutex-cherrypickjimingham/from-apple-llvm-project:fixup-stack-writer-mutex-cherrypickCopy head branch name to clipboard