Disable -Wmismatched-tags for mesa.
Disable -Wmismatched-tags for mesa.

We build with 3rd-party code with -Wall on the clang/win bot. This has already
been fixed upstream, so there's no need to keep this around

https://github.com/grate-driver/mesa/commit/68a4bb553bcd51d336d95b0c845c0dc63adc3bd3

BUG=none
R=hans@chromium.org
TBR=cpu

Review URL: https://codereview.chromium.org/470313002

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@289680 0039d316-1c4b-4281-b951-d872f2087c98

littlstar/chromium.src,ondra-novak/chromium.src,ondra-novak/chromium.src,littlstar/chromium.src,ondra-novak/chromium.src,bright-sparks/chromium-spacewalk,bright-sparks/chromium-spacewalk,ondra-novak/chromium.src,bright-sparks/chromium-spacewalk,ondra-novak/chromium.src,bright-sparks/chromium-spacewalk,littlstar/chromium.src,bright-sparks/chromium-spacewalk,littlstar/chromium.src,littlstar/chromium.src,littlstar/chromium.src,ondra-novak/chromium.src,bright-sparks/chromium-spacewalk,ondra-novak/chromium.src,bright-sparks/chromium-spacewalk,bright-sparks/chromium-spacewalk,littlstar/chromium.src,littlstar/chromium.src,ondra-novak/chromium.src,ondra-novak/chromium.src,bright-sparks/chromium-spacewalk