Merge "Revert "libc: point some x86_64 function impls at llvm-libc"" into main am: 5aa7333238

Original change: https://android-review.googlesource.com/c/platform/bionic/+/3361726

Change-Id: I2836024dd15f0d700eab91d16f535c4843f37034
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>