[clang] [clang] Add `intrin0.h` header to mimic `intrin0.h` used by MSVC STL for clang-cl (PR #75711)

[Nico Weber via cfe-commits]

nico wrote:

Looks like it belongs to MSVC: https://github.com/microsoft/STL/blob/a8888806c6960f1687590ffd4244794c753aa819/stl/inc/yvals_core.h#L2040

So I think the right order here is:

1. Add intrin0.h header
2. Wait for a release
3. Change MSSTL to include that in clang builds as well
4. Wait for a release of that
5. Make intrin.h the chonky header

If we land this as-is, it'll tank build time on Windows.

https://github.com/llvm/llvm-project/pull/75711