Switch off maybe-uninitialized warning as it gives often
false positives with optimizations in gcc.

NOTRY=true
TBR=bmeurer@chromium.org, zhengxing.li@intel.com, caitp@igalia.com, ahaas@chromium.org

Committed: https://crrev.com/0ef0d5b2b8cffd1e3647d79c5ba19752bbbc469c
Review-Url: https://codereview.chromium.org/2425913002
Cr-Original-Commit-Position: refs/heads/master@{#40382}
Cr-Commit-Position: refs/heads/master@{#40394}