[COFF, ARM64] Implement Intrinsic.sponentry for AArch64

Summary: This patch adds Intrinsic.sponentry. This intrinsic is required to correctly support setjmp for AArch64 Windows platform.

Patch by: Yin Ma (yinma@codeaurora.org)

Reviewers: mgrang, ssijaric, eli.friedman, TomTan, mstorsjo, rnk, compnerd, efriedma

Reviewed By: efriedma

Subscribers: efriedma, javed.absar, kristof.beyls, chrib, llvm-commits

Differential Revision: https://reviews.llvm.org/D53996

llvm-svn: 345909