[compiler-rt] [ASan] Update meminstrinsics to use library memmove rather than internal (PR #160740)

[Dan Blackwell via llvm-commits]

DanBlackwell wrote:

> LGTM - do we need tests for this so it doesn't regress?

I can't see any tests for the memintrinsics stuff; do you think there's anything that we could be testing here @melver?

https://github.com/llvm/llvm-project/pull/160740