[clang] [clang][AIX] Fix -print-runtime-dir fallback on AIX (PR #141439)

[Daniel Chen via cfe-commits]

DanielCChen wrote:

Another related question but not necessarily in the scope of this PR:
It seems both `aix-ld.c` and `aix-rtlib.c` still have the "old" OS path in test. They all pass though after we change the default to per target for `libclang_rt*.a`. Is it expected? If so, should the change of test in this PR void? @daltenty 

https://github.com/llvm/llvm-project/pull/141439