[clang] [clang][ARM][AArch64] Don't require arm_acle header for universally defined intrinsics (PR #136742)

[Reid Kleckner via cfe-commits]

rnk wrote:

Sure, but winnt.h declares and uses tons of x86 intrinsics already, and we have a way to make this work. Let me go look at what we did for `_m_prefetchw` and see if we can apply that here.

We want to do something similar to a default-error-warning, where system headers like winnt.h are allowed to be non-portable (use the MSVC intrinsic model), but we push users to write portable code by including the relevant portable intrinsic header (arm_acle.h).

https://github.com/llvm/llvm-project/pull/136742