[AArch64][GlobalISel] Select @llvm.aarch64.stlxr for 32-bit pointers
Add partial instruction selection for intrinsics like this:
declare i32 @llvm.aarch64.stlxr(i64, i32*)
(This only handles the case where a G_ZEXT is feeding the intrinsic.)
Also make sure that the added store instruction actually has the memory op from
the original G_STORE.
Update select-stlxr-intrin.mir and arm64-ldxr-stxr.ll.
Differential Revision: https://reviews.llvm.org/D65355