[clang] [llvm] [flang-rt] Pass the whole path of libflang_rt.runtime.a to linker on AIX (PR #131041)

[Daniel Chen via llvm-commits]

DanielCChen wrote:

The intention is to make this PR for flang-rt only. As discussed with @daltenty, I remove the NFC-change of adding an overriding `getCompilerRT` in `AIX.cpp` as it actually breaches into clang space.

https://github.com/llvm/llvm-project/pull/131041