track local aosp based gcc repo [1/2]

Summary:
contains 4.6, 4.7, and 4.8 repos.
This change makes it easier to merge good
changes upstream as well as moving us to
utilizing stable release tags only.

Test Plan: win

Reviewers: randall.rushing, synergy

Reviewed By: synergy

Differential Revision: http://review.codefirex.com/D385

Change-Id: Ice7263bb5265c47cf4fdb2ec3c04b398f5093788