[clang] [Draft][Clang][HIP] Guard declarations of `cmath` comparisons when using Microsoft's STL (PR #200395)

[Juan Manuel Martinez Caamaño via cfe-commits]

jmmartinez wrote:

Abandoned in favor of https://github.com/llvm/llvm-project/pull/201563 which should be easier to maintain.

https://github.com/llvm/llvm-project/pull/200395