Turn off buffer security checking in Release builds.

Turn off buffer security checking in Release builds.

I'm seeing /GS's _security_check_cookie() show up as a signficant piece of time when profiling.  That's mostly just annoying noise.  We generally use our Release builds for performance testing and Debug for correctness, so it seems like a fair thing to disable in Release builds... it's a sort of ASAN thing, which we only do in Debug on other platforms.

BUG=skia:

GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=3782

Change-Id: I9b3cf4c5cf943fc2549f5bf91a1f6f7e41733e2c
Reviewed-on: https://skia-review.googlesource.com/3782
Commit-Queue: Mike Klein <mtklein@chromium.org>
Reviewed-by: Ben Wagner <bungeman@google.com>