Move perf test common files to a source set. Similarly to a prior patch this organizes the common perf test sources into a single target. This will allow us to more easily support setting compiler flags on particular perf test sources. This also fixes some build errors that popped up when new warnings were enabled. Bug: angleproject:3630 Change-Id: I866885199f93a5055e8d160e39f72d1f8209bc75 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2103086 Commit-Queue: Jamie Madill <jmadill@chromium.org> Reviewed-by: Yuly Novikov <ynovikov@chromium.org>