Introduce element-wise atomic memcpy intrinsic

This change adds a new intrinsic which is intended to provide memcpy functionality
with additional atomicity guarantees. Please refer to the review thread
or language reference for further details.

Differential Revision: https://reviews.llvm.org/D27133



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@290708 91177308-0d34-0410-b5e6-96231b3b80d8
8 files changed