And fix issues where global variables would not be emitted unless they were transitively referenced by an entry point.
This change requires crbug.com/tint/697 to be fixed before landing.
Change-Id: I712bd9d369e08c9a3cdfb0f114c3609584f91f28
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/54241
Kokoro: Kokoro <noreply+kokoro@google.com>
Reviewed-by: James Price <jrprice@google.com>