Roll to GCC 4.9.2

    Picked changes from branch svn-mirror/google/gcc-4_9-mobile at
      commit 952223c94dee89f9c4e6b39fa752627cf1af8936

BUG=chromium:460557
TEST=cbuildbots: chromiumos-sdk, several boards for each platform.
     hwtest and some kernel testing.
     Tested on projects that had issues with previous roll:
       Flash, chromoting, chromecast, breakpad
     Verified performance (small improvements on ARM).
CQ-DEPEND=CL:254610

Change-Id: I17b787562088f0c298efdc224695e521001d7e74
Reviewed-on: https://chromium-review.googlesource.com/246732
Reviewed-by: Mike Frysinger <vapier@chromium.org>
Tested-by: Luis Lozano <llozano@chromium.org>
741 files changed