[COFF, ARM64] Add __byteswap intrinsics

Reviewers: rnk, efriedma, ssijaric, TomTan, haripul

Reviewed By: efriedma

Subscribers: javed.absar, cfe-commits, kristof.beyls

Differential Revision: https://reviews.llvm.org/D56685

llvm-svn: 351147