This will allow us to more easily support a different test target
topology for the standalone test harness that uses an intermediate
source_set. Also it's better in the long run to only have to worry
about one set of EGL headers.
Bug: angleproject:3162
Change-Id: I738dbb68df1abc0c0569748e18d6826914d90a52
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2233399Reviewed-by: Jonah Ryan-Davis <jonahr@google.com>
Commit-Queue: Jamie Madill <jmadill@chromium.org>
