[msan] Add avx512-intrinsics.ll and avx512-intrinsics-upgrade.ll test case (#123980)

These are forked from the corresponding files in llvm/test/CodeGen/X86/.

avx512-intrinsics.ll shows that many intrinsics are already
heuristically handled by MSan, and can be used to track refinements to
the intrinsic handling.

avx512-intrinsics-upgrade.ll tests intrinsics that LLVM "auto-upgrades";
for example, @llvm.x86.avx512.mask.store is converted into
@llvm.masked.store (which has the interesting side effect that
MemorySanitizer can already handle it via its existing
handleMaskedStore).

Author: thurstond