swift

7fcc8a54 - [frontend] Expose via a LangOption whether or not the compiler is compiling for a triple that supports AArch64 TBI.

[frontend] Expose via a LangOption whether or not the compiler is compiling for a triple that supports AArch64 TBI. Just breaking down layers of a larger patch to make it easier to review. (cherry picked from commit bfecaa357f5b9f1bb6f8eac12cb43c1ea4956d7e)