GCC: move warm up tasks out of anonymous namespace GCC anonymous namespace is set per file. So forward declaring in the anonymous namespace of .h will not be valid in the .cpp file. Bug: chromium:40565911 Change-Id: I10bd94f035761602d69e59a94dfde5dc774a6776 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/5475346 Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org> Reviewed-by: Charlie Lao <cclao@google.com> Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>