Prepare upcoming GCC 4.8 release.

o Add -Wno-unused-parameter -Wno-unused-but-set-parameter to suppress
  new warnings.
o Define GCC_COLORS to enable colorful diagnostic messages.

Change-Id: Icbd62300b0e6f39d4e514edec2431a06b4d72421
(cherry picked from internal commit ccd8e6082b5b1e519a75068fa6c887a1a85b53c4)
Add missing LOCAL_ADDITIONAL_DEPENDENCIES dependency to BUILD_PREBUILT.

Change-Id: Id7c0e77110653e618d783026cd4b4aeadb3c45ec