[safestack] Enable loongarch64

Enable safestack on loongarch64.

Some test cases will fail on loongarch, it will be fixed in glibc,
Links: https://sourceware.org/pipermail/libc-alpha/2022-November/143641.html

Reviewed By: #sanitizers, SixWeining, vitalybuka

Differential Revision: https://reviews.llvm.org/D139494