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