[AArch64] Support for memset tagged intrinsic

This introduces a new ACLE intrinsic for memset tagged
(https://github.com/ARM-software/acle/blob/next-release/main/acle.md#memcpy-family-of-operations-intrinsics---mops).

  void *__builtin_arm_mops_memset_tag(void *, int, size_t)

A corresponding LLVM intrinsic is introduced:

  i8* llvm.aarch64.mops.memset.tag(i8*, i8, i64)

The types match llvm.memset but the return type is not void.

This is part 1/4 of a series of patches split from
https://reviews.llvm.org/D117405 to facilitate reviewing.

Patch by Tomas Matheson

Differential Revision: https://reviews.llvm.org/D117753