Change proxied Makefile dependencies to .h.

The third_party dependencies gtest/gmock and libevent are less
confusing when they are proxied by their header files. The compiled
libraries are included implicitly (like the header files before).

Change-Id: Ieb0eae473adfb9811214a40df8334c541e6ff9a3
BUG: 26564098
Reviewed-on: https://weave-review.googlesource.com/2237
Reviewed-by: Vitaly Buka <vitalybuka@google.com>
diff --git a/Makefile b/Makefile
index ebc8c4c..512c2a6 100644
--- a/Makefile
+++ b/Makefile
@@ -84,8 +84,8 @@
 
 weave_obj_files := $(WEAVE_SRC_FILES:%.cc=out/$(BUILD_MODE)/%.o)
 
-# TODO(jacobmarble): There are too many libgtest.a deps in non-test targets. Fix.
-$(weave_obj_files) : out/$(BUILD_MODE)/%.o : %.cc third_party/lib/libgtest.a
+# TODO(jacobmarble): There are too many gtest/gmock deps in non-test targets. Fix.
+$(weave_obj_files) : out/$(BUILD_MODE)/%.o : %.cc third_party/include/gtest/gtest.h
 	mkdir -p $(dir $@)
 	$(CXX) $(DEFS_$(BUILD_MODE)) $(INCLUDES) $(CFLAGS) $(CFLAGS_$(BUILD_MODE)) $(CFLAGS_CC) -c -o $@ $<