[llvm] [Hexagon] Omit calls to specialized {float, fix} routines (PR #117423)

[Brian Cain via llvm-commits]

androm3da wrote:

@SundeepKushwaha these functions are provided in `libqcc` but that's not provided by the upstream toolchain.

Also: I think it's the case that `clang` might not permit int128 references.  But other compilers can.

This issue was raised while contributing hexagon specializations for other builtins to zig - see https://github.com/ziglang/zig/pull/22029

https://github.com/llvm/llvm-project/pull/117423