hardware/interfaces: Android.mk always -Werror

Bug: 35840847
Test: pass
Change-Id: I6ebf3f5d279ff405446592cdabaeca9d1fdf6cf9
diff --git a/core/config.mk b/core/config.mk
index 7709d3c..968c0de 100644
--- a/core/config.mk
+++ b/core/config.mk
@@ -817,6 +817,7 @@
     art/% \
     bionic/% \
     external/fio/% \
+    hardware/interfaces/% \
 
 define find_warning_disallowed_projects
     $(filter $(ANDROID_WARNING_DISALLOWED_PROJECTS),$(1)/)