Upgrade x86 gcc to 4.9 and disable devirtualization.

Also filter out gcc-only flags -Wno-clobbered and -fno-devirtualize
when compiled with clang/llvm.

BUG: 19872411
Change-Id: I6de57583be04da607f569df65e93531787dbb789
(cherry picked from AOSP commit 90036610ddfe0455553a1b46bb8adbeafde0cac1)

3 files changed