do not hardcode -I/usr/include

There is no reason to force -I/usr/include, and doing so breaks cross-
compiles.  Punt the flag from all build files.

BUG=chromium:488360
TEST=precq passes

Change-Id: Ia8b7d3ae8a1ace4e4a71d31d7a15ed7a49d14760
Reviewed-on: https://chromium-review.googlesource.com/271640
Trybot-Ready: Mike Frysinger <vapier@chromium.org>
Tested-by: Mike Frysinger <vapier@chromium.org>
Reviewed-by: Darren Krahn <dkrahn@chromium.org>
Commit-Queue: Mike Frysinger <vapier@chromium.org>
18 files changed