[llvm] [X86][CodeGen] Restrict F128 lowering to GNU environment (PR #81664)

[Arthur Eubanks via llvm-commits]

aeubanks wrote:

can you link to #79611 in the description?

shouldn't this update `llvm/test/CodeGen/X86/fp128-libcalls.ll`, which has a test with `-mtriple=x86_64-linux-android`?

https://github.com/llvm/llvm-project/pull/81664