Add LOCAL_AAPT2_ONLY

This allows modules to specify that they may only be used from modules
using aapt2. Using aapt2 removes absolute path references to modules, so
this can be useful if a module is preparing to move its sources, or
replace itself with a prebuilt aar.

Test: m
Test: Label frameworks/support/design; m
Test: Label frameworks/support/v4; m
Test: build/soong/build_test.bash
Change-Id: Icfb3d4b19a6a0e3a3bb00091d2a97a4d88c0c761
diff --git a/core/clear_vars.mk b/core/clear_vars.mk
index 1e64c4f..bd605ec 100644
--- a/core/clear_vars.mk
+++ b/core/clear_vars.mk
@@ -4,6 +4,7 @@
 
 # '',true
 LOCAL_32_BIT_ONLY:=
+LOCAL_AAPT2_ONLY:=
 LOCAL_AAPT_FLAGS:=
 LOCAL_AAPT_INCLUDE_ALL_RESOURCES:=
 LOCAL_ADDITIONAL_CERTIFICATES:=