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Add various cflags/cflags_cc and disable clang chromium-style
enforcement on third_party/khronos_glcts sourcecode and support.

This is a workaround for various compile time warnings on desktop
linux (e.g. Ubuntu 12.04) that are treated as errors (i.e. by
-Werror).  The source of these warnings are from the
third_party/khronos_glcts sourcecode.  With these workarounds
the khronos_glcts_test is able to finish compilation.

The plan is to eventually fix the third-party code so we can
remove these workarounds.

BUG=chromium:412865
R=piman@chromium.org, kbr@chromium.org
TBR=piman@chromium.org
TEST=export GYP_DEFINES="internal_khronos_glcts_tests=1"
TEST=gclient runhooks
TEST=ninja -C out/Release khronos_glcts_test
TEST=./out/Release/khronos_glcts_test
TEST=ninja -C out/Debug khronos_glcts_test
TEST=./out/Debug/khronos_glcts_test
Signed-off-by: U. Artie Eoff <ullysses.a.eoff@intel.com>

Review URL: https://codereview.chromium.org/615063004

Cr-Commit-Position: refs/heads/master@{#297929}