[clang] [clang][AIX] Handle triple environment component for per target runtime directory (PR #140850)

[Daniel Chen via cfe-commits]

DanielCChen wrote:

A more general question:
It seems neither `compile-rt` nor `flang-rt` uses `getTargetSubDirPath`, so we didn't need to strip to the "base" triple.
Sanitizer uses it apparently. Is it by design? @daltenty 

https://github.com/llvm/llvm-project/pull/140850