linkage_checker: ignore broken linkage with LLVM libc++.
linkage_checker: ignore broken linkage with LLVM libc++.

This linkage will be broken in LLVM 15, but this is typically harmless
since dyld will load `/usr/lib/libc++.1.dylib` instead.

Homebrew/brew,MikeMcQuaid/brew,MikeMcQuaid/brew,Homebrew/brew,MikeMcQuaid/brew,Homebrew/brew,nandub/brew,MikeMcQuaid/brew,nandub/brew,JCount/brew,nandub/brew,nandub/brew,JCount/brew,JCount/brew,Homebrew/brew,JCount/brew