ImageHelper::barrierImpl with secondary command buffer is used in
other translation units. Linking fails if compiler has optimized
out symbol for secondary command buffer.

Bug: angleproject:5324
Change-Id: I588d0d949a9b2eee04d8103effc485ab23d679c6
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2526082Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>