Dawn needs to know if a given entry point uses this builtin, so that
it can pass this information via a root constant for HLSL.
Bug: tint:752
Change-Id: I8bcd3a343db16774ffedd9db9813451f97f10aba
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/64040
Kokoro: Kokoro <noreply+kokoro@google.com>
Reviewed-by: Ben Clayton <bclayton@google.com>