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

[Alexandre Ganea via llvm-commits]

aganea wrote:

@stefan-il Please see discussion in https://reviews.llvm.org/D101427 especially last comment by @MaskRay. We could encode those linker flags for ease of use perhaps, when LLVM_ENABLE_RPMALLOC is used, if someone wants to do it.

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