[Clang] Add `__CLANG_GPU_DISABLE_MATH_WRAPPERS` macro for offloading math (#98234)

Summary:
Currently we replace all math calls with vendor specific ones. This
patch introduces a macro `__CLANG_GPU_DISABLE_MATH_WRAPPERS` that when
defined will disable this.

I went this route instead of a flag for two reasons. One, I think we
have too many flags as is, and we already have `-nogpuinc` to cover
disabling these wrappers entirely, so this would be a really specific
subset of that. Second, these math headers aren't easily decoupled by
simply not including a single header from the clang driver layer.
There's the cmath and the regular math forward declares it would disable
as well.

Note, this currently causes errors because the GPU `libm` doesn't have
`powi`, that's an NVIDIA extension I'll add to LLVM libm.

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