bootcache: remove Wformat from common.mk

The Makefile has "CFLAGS += -Wformat=0", the common.mk has
"COMMON_CFLAGS :=  -Wall -Werror -fno-strict-aliasing -O1  -Wformat=2"
This one overides the CFLAGS in make file and cause clang syntax check
fail.
BUG=chromium:230617
TEST=CFLAGS="-clang -print-cmdline" CXXFLAGS="-clang -print-cmdline"
      emerge-x86-alex bootcache passes

Change-Id: Ia68b70f890dad8152b741d2ee39724a1fe412fc8
Reviewed-on: https://gerrit.chromium.org/gerrit/47915
Reviewed-by: Paul Taysom <taysom@chromium.org>
Commit-Queue: Yunlian Jiang <yunlian@chromium.org>
Tested-by: Yunlian Jiang <yunlian@chromium.org>
1 file changed