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

[Max Winkler via cfe-commits]

MaxEW707 wrote:

Just want to say thanks for everyone taking the time to review the PR and providing feedback :).
Looking forward to using this in the next release of clang-cl.

> I'm a bit worried that we don't have any test coverage for this file to begin with, so it's a bit hard to validate that the changes are correct, but we're early enough in a release cycle that I think we'll get feedback with plenty of time to address unintentional fallout.

I'll look into adding unit tests next week in a separate PR. If not it will be closer towards the end of March due to personal things.
If any issues pop up feel free to @ me. I don't intend to commit and dash :).

> The changes should come with a release note in clang/docs/ReleaseNotes.rst so that users know about the compile time performance improvements.

Done. Feel free to reword the release notes as necessary. I believe I landed on something that is informative but succinct. 

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