To still produce the class-memaccess diagnostic on unintended cases,
suppress it only for our Memset<T> case and LLVM.

Bug: b/135744933
Change-Id: Id3b421a3b831600097d198ac793f582467d0a520
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/33429
Presubmit-Ready: Nicolas Capens <nicolascapens@google.com>
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>
Tested-by: Nicolas Capens <nicolascapens@google.com>
Reviewed-by: Ben Clayton <bclayton@google.com>