Provide mechanism to override llvm-rs-cc headers.

Change-Id: I87fd496069a9dfde633e2d232e436fa5d7315cc0
diff --git a/core/clear_vars.mk b/core/clear_vars.mk
index bc085f5..1b9bb8a 100644
--- a/core/clear_vars.mk
+++ b/core/clear_vars.mk
@@ -104,6 +104,7 @@
 LOCAL_WARNINGS_ENABLE:=
 LOCAL_MANIFEST_FILE:=
 LOCAL_RENDERSCRIPT_INCLUDES:=
+LOCAL_RENDERSCRIPT_INCLUDES_OVERRIDE:=
 LOCAL_RENDERSCRIPT_CC:=
 LOCAL_BUILD_HOST_DEX:=
 LOCAL_DEX_PREOPT:=