Fix link validation with ambiguous instanceless interface blocks The following interface blocks should fail link: VS: layout(binding=0) buffer BufferBlockNameA { mediump float variable; }; FS: layout(binding=1) buffer BufferBlockNameB { mediump float variable; }; Because `variable` is ambiguous. Bug: angleproject:3580 Change-Id: I29576a6f152780819af0e9fb63249dbee7d9f2fc Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2587450 Reviewed-by: Jamie Madill <jmadill@chromium.org> Reviewed-by: Tim Van Patten <timvp@google.com> Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>