[clang] [llvm] Add support for Windows hot-patching (PR #138972)

[Alexandre Ganea via llvm-commits]

aganea wrote:

Oh so all this dance (`_ref_` and the additional metadata) is for code page integrity purposes? To keep them unmodified in memory? So how does then the kernel use the PE metadata if it doesn't patch the code memory pages of the initial (running) image? Is there an additional mechanism for trapping and redirecting calls into the new image? If that's the case, there's no really image patching involved at runtime? The "hot-patching" is just a _vue d'esprit_ to present the concept to the user?

https://github.com/llvm/llvm-project/pull/138972