[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.

Reviewers: mgrang, TomTan, rnk, compnerd, mstorsjo, efriedma

Reviewed By: efriedma

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

Differential Revision: https://reviews.llvm.org/D53673

llvm-svn: 345791