[clang] [Clang] Set the FTM for trivial relocation (PR #142936)

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EricWF wrote:

@cor3ntin I think Apple Clang still  complicates version detection, and we can't use `__has_builtin`, because that's returned true for version of Clang where it's "broken" from libc++'s perspective. 

I don't think @ldionne would feel comfortable shipping actual libc++ changes if the compiler doesn't feel comfortable with it's own implementation.

https://github.com/llvm/llvm-project/pull/142936