v8: -Werror is no longer disabled

[bnoordhuis]

Today's master builds V8 with -Werror. Excerpt from ./configure --gdb && make -C out BUILDTYPE=Debug:

  g++ '-DOPENSSL_NO_SSL2=1' '-DV8_TARGET_ARCH_X64' '-DENABLE_DEBUGGER_SUPPORT' '-DENABLE_GDB_JIT_INTERFACE' '-DDEBUG' '-D_DEBUG' '-DENABLE_DISA
SSEMBLER' '-DV8_ENABLE_CHECKS' '-DOBJECT_PRINT' '-DVERIFY_HEAP' '-DENABLE_EXTRA_CHECKS' '-DENABLE_HANDLE_ZAPPING' -I../deps/v8/src  -pthread -W
all -Wextra -Wno-unused-parameter -m64 -fno-strict-aliasing -m64 -g -Wall -Werror -W -Wno-unused-parameter -Wnon-virtual-dtor -Woverloaded-virt
ual -fdata-sections -ffunction-sections -fno-rtti -fno-exceptions -MMD -MF /home/bnoordhuis/src/master/out/Debug/.deps//home/bnoordhuis/src/mas
ter/out/Debug/obj.target/v8_base.x64/deps/v8/src/accessors.o.d.raw  -c -o /home/bnoordhuis/src/master/out/Debug/obj.target/v8_base.x64/deps/v8/
src/accessors.o ../deps/v8/src/accessors.cc

Building with gcc-4.8 breaks the build because of -Wunused-local-typedefs warnings turned to errors.