[clang] [clang][Driver] Define soft float macros for PPC. (PR #106012)

[Qiu Chaofan via cfe-commits]

ecnelises wrote:

Could you pick the test change from https://github.com/ecnelises/llvm-project/commit/9dcb9c96d565f282ca716693b37c65674c3f7edd into this patch?

https://github.com/llvm/llvm-project/pull/106012