libweave: Add clang support to Makefile.

To use: "CLANG=1 make all -j"

BUG: 26508278

Change-Id: I6b09e6574634d8e07ce2438c31907466e953eb0f
Reviewed-on: https://weave-review.googlesource.com/2185
Reviewed-by: Vitaly Buka <vitalybuka@google.com>
diff --git a/tests.mk b/tests.mk
index 64fc622..aa9ee53 100644
--- a/tests.mk
+++ b/tests.mk
@@ -23,7 +23,7 @@
 	$(CXX) $(DEFS_$(BUILD_MODE)) $(INCLUDES) $(CFLAGS) $(CFLAGS_$(BUILD_MODE)) $(CFLAGS_CC) -c -o $@ $<
 
 out/$(BUILD_MODE)/libweave_testrunner : $(weave_unittest_obj_files) $(third_party_chromium_crypto_unittest_obj_files) $(third_party_chromium_base_unittest_obj_files) out/$(BUILD_MODE)/libweave_common.a out/$(BUILD_MODE)/libweave-test.a
-	$(CXX) -o $@ $^ -lcrypto -lexpat -lgmock -lgtest -lpthread -lrt -Lthird_party/lib
+	$(CXX) -o $@ $^ $(CFLAGS) -lcrypto -lexpat -lgmock -lgtest -lpthread -lrt -Lthird_party/lib
 
 test : out/$(BUILD_MODE)/libweave_testrunner
 	$<
@@ -39,7 +39,7 @@
 	$(CXX) $(DEFS_$(BUILD_MODE)) $(INCLUDES) $(CFLAGS) $(CFLAGS_$(BUILD_MODE)) $(CFLAGS_CC) -c -o $@ $<
 
 out/$(BUILD_MODE)/libweave_exports_testrunner : $(weave_exports_unittest_obj_files) out/$(BUILD_MODE)/libweave.so out/$(BUILD_MODE)/libweave-test.a out/$(BUILD_MODE)/src/test/weave_testrunner.o
-	$(CXX) -o $@ $^ -lcrypto -lexpat -lgmock -lgtest -lpthread -lrt -Lthird_party/lib -Wl,-rpath=out/$(BUILD_MODE)/
+	$(CXX) -o $@ $^ $(CFLAGS) -lcrypto -lexpat -lgmock -lgtest -lpthread -lrt -Lthird_party/lib -Wl,-rpath=out/$(BUILD_MODE)/
 
 export-test : out/$(BUILD_MODE)/libweave_exports_testrunner
 	$<