obey --enable-werror when building clang plugin

Change-Id: I8ca9b09a6ffd4b2f00740563fa9682fdabb26b3d
diff --git a/compilerplugins/Makefile-clang.mk b/compilerplugins/Makefile-clang.mk
index 04b938f..3e7ef93 100644
--- a/compilerplugins/Makefile-clang.mk
+++ b/compilerplugins/Makefile-clang.mk
@@ -31,6 +31,10 @@ CLANGOUTDIR=$(BUILDDIR)/compilerplugins/obj

QUIET=$(if $(VERBOSE)$(verbose),,@)

ifneq ($(EXTERNAL_WARNINGS_NOT_ERRORS),TRUE)
CLANGWERROR := -Werror
endif

compilerplugins: compilerplugins-build

# The list of source files, generated automatically (all files in clang/, but not subdirs).
@@ -69,7 +73,7 @@ CLANGOBJS=
define clangbuildsrc
$(3): $(2) $(SRCDIR)/compilerplugins/Makefile-clang.mk $(CLANGOUTDIR)/clang-timestamp
	@echo [build CXX] $(subst $(SRCDIR)/,,$(2))
	$(QUIET)$(CXX) $(CLANGCXXFLAGS) $(CLANGDEFS) $(CLANGINCLUDES) -I$(BUILDDIR)/config_host $(2) -fPIC -std=c++11 -c -o $(3) -MMD -MT $(3) -MP -MF $(CLANGOUTDIR)/$(1).d
	$(QUIET)$(CXX) $(CLANGCXXFLAGS) $(CLANGWERROR) $(CLANGDEFS) $(CLANGINCLUDES) -I$(BUILDDIR)/config_host $(2) -fPIC -std=c++11 -c -o $(3) -MMD -MT $(3) -MP -MF $(CLANGOUTDIR)/$(1).d

-include $(CLANGOUTDIR)/$(1).d