Generate header file dependencies

Gcc/clang with -MMD can generates make style dependencies.

BUG:26572623
Change-Id: Iae7461a361d7b21df3a782b7f487aa9faadffbae
Reviewed-on: https://weave-review.googlesource.com/2195
Reviewed-by: Jacob Marble <jacobmarble@google.com>

Makefile

diff --git a/Makefile b/Makefile
index 911f106..d08be68 100644
--- a/Makefile
+++ b/Makefile
@@ -66,6 +66,11 @@
   endif
 endif
 
+# Headers dependencies.
+CFLAGS += -MMD
+OBJFILES = $(shell find out/$(BUILD_MODE)/ -type f -name '*.o')
+-include $(OBJFILES:.o=.d)
+
 ###
 # libweave.so