Enable -Wall/-Werror with LOCAL_RENDERSCRIPT_FLAGS.

Change-Id: Ia2a058e6711839d89072c2e96f0c60aa4cedda6b
diff --git a/core/clear_vars.mk b/core/clear_vars.mk
index d9f3372..3a04b7b 100644
--- a/core/clear_vars.mk
+++ b/core/clear_vars.mk
@@ -107,6 +107,7 @@
 LOCAL_RENDERSCRIPT_INCLUDES:=
 LOCAL_RENDERSCRIPT_INCLUDES_OVERRIDE:=
 LOCAL_RENDERSCRIPT_CC:=
+LOCAL_RENDERSCRIPT_FLAGS:=
 LOCAL_RENDERSCRIPT_TARGET_API:=
 LOCAL_BUILD_HOST_DEX:=
 LOCAL_DEX_PREOPT:= # '',true,false,nostripping