[llvm] [Support] Vendor rpmalloc in-tree and use it for the Windows 64-bit release (PR #91862)

[via llvm-commits]

https://github.com/zmodem commented:

> > I think there are still some unresolved comments from my review, but I'm all for getting this merged.
> 
> @zmodem Could you please point me specifically to which comments were unresolved? I think I’ve answered here: [#91862 (comment)](https://github.com/llvm/llvm-project/pull/91862#issuecomment-2107491507)

Sorry, my fault. It seems my comments were still "pending" :(

https://github.com/llvm/llvm-project/pull/91862