Add -g/--build option to for-all-touched-files.py

Add -g/--build option to for-all-touched-files.py

This option will be useful for updating build files with
tools/sort_sources.py, like:

  tools/git/for-all-touched-files.py -g "tools/sort_sources.py [[FILENAME]]"

BUG=456014
TEST=modify some files, confirm the new option worked as expected

Committed: https://crrev.com/80e88d555ecba67b08727ac35e0c2543e9a84532
Cr-Commit-Position: refs/heads/master@{#316512}

[satorux1, 2015-02-16 03:21:56]

satorux@chromium.org changed reviewers:
+ derat@chromium.org

[Daniel Erat, 2015-02-16 23:28:29]

lgtm

[satorux1, 2015-02-16 23:48:25]

The CQ bit was checked by satorux@chromium.org

[commit-bot: I haz the power, 2015-02-16 23:49:04]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/934473003/1

[commit-bot: I haz the power, 2015-02-16 23:51:27]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-02-16 23:52:22]

Patchset 1 (id:??) landed as
https://crrev.com/80e88d555ecba67b08727ac35e0c2543e9a84532
Cr-Commit-Position: refs/heads/master@{#316512}