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 90036610dd)

core/clang/config.mk

@@ -68,12 +68,15 @@ CLANG_CONFIG_UNKNOWN_CFLAGS := \
   -finline-functions \
   -finline-limit=64 \
   -fno-canonical-system-headers \
+  -Wno-clobbered \
+  -fno-devirtualize \
   -fno-tree-sra \
   -fprefetch-loop-arrays \
   -funswitch-loops \
   -Werror=unused-but-set-parameter \
   -Werror=unused-but-set-variable \
   -Wmaybe-uninitialized \
+  -Wno-error=clobbered \
   -Wno-error=maybe-uninitialized \
   -Wno-error=unused-but-set-parameter \
   -Wno-error=unused-but-set-variable \