[clang] [flang] [flang] Fixes for LIT testing of FLANG_RUNTIME_F128_MATH_LIB build. (PR #82832)

[Slava Zakharin via cfe-commits]

vzakhari wrote:

I do not think the Windows CI failure has anything to do with my changes.  I am going to merge this.

https://github.com/llvm/llvm-project/pull/82832