Deqp gyp use_x11 fixes. Remove the use_x11==1 condition from two things which have nothing to do with x11: defining _GNU_SOURCE and choosing deqp_libtester_sources_unix. This lets us build for Chrome OS where typically use_x11==0. BUG=angleproject:1297 Change-Id: I9166f2a8119493aaab82af15e109d378fffb811a Reviewed-on: https://chromium-review.googlesource.com/337695 Reviewed-by: Jamie Madill <jmadill@chromium.org> Reviewed-by: Corentin Wallez <cwallez@chromium.org> Commit-Queue: Frank Henigman <fjhenigman@chromium.org>