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)
Re-tighten default compiler options.

Remove "-Wno-unused-parameter -Wno-unused-but-set-parameter" added for
GCC 4.8 experiment.

BUG: 10495043
(cherry picked from internal master 1cea0755f400c1d183d22679d5b931c3a04ae4a4)

Change-Id: Ifa221709b1351a9268c06872e2b667138995c3da