tools: Make YCM config aware of sysroot image.

We use a sysroot image on linux so we should make YCM aware of it by
parsing the --sysroot= compile flag.

BUG=NONE
R=asanka@chromium.org

Review URL: https://codereview.chromium.org/1669073002

Cr-Original-Commit-Position: refs/heads/master@{#375211}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 3a2e1e8ed11cf39674111fb137b9bf2190b9b089
3 files changed