[clang] [llvm] Support the inline asm 'a' constraint on PowerPC (PR #141604)

[Kamau Bridgeman via cfe-commits]

kamaub wrote:

After discussion with the IBM llvm on power team I will separate the type promotion error test case file into another patch as the error is only exposed by, not caused by this patch.

https://github.com/llvm/llvm-project/pull/141604