x86/build: Remove cc-option from -mno-fp-ret-in-387

x86/build: Remove cc-option from -mno-fp-ret-in-387

This has been supported in GCC for forever and clang gained support for it as
an alias of '-mno-x87' in LLVM 14. Now that x86 requires LLVM 15 or newer
since

  7861640aac52 ("x86/build: Raise the minimum LLVM version to 15.0.0"),

this flag can be unconditionally added, saving a compiler invocation.

Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://github.com/llvm/llvm-project/commit/a9fba2be35db674971382e38b99a31403444d9bf
Link: https://lore.kernel.org/20250814-x86-min-ver-cleanups-v1-4-ff7f19457523@kernel.org