Default to enable tidy warnings in header files.

Change-Id: I3831f03facbbd6d17117d82f9ccac49bc2645237
diff --git a/core/binary.mk b/core/binary.mk
index 614b8aa..f13689a 100644
--- a/core/binary.mk
+++ b/core/binary.mk
@@ -1419,6 +1419,10 @@
     ifneq ($(LOCAL_TIDY_FLAGS),)
       my_tidy_flags := $(LOCAL_TIDY_FLAGS)
     endif
+    # If tidy flags are not specified, default to check all header files.
+    ifeq ($(my_tidy_flags),)
+      my_tidy_flags := -header-filter=.*
+    endif
   endif
 endif