Allow locally disabling R8

Bug: 74746744
Test: m checkbuild
Change-Id: I5741f15821cf8de5df494ed8ad31d32a44657514
diff --git a/core/clear_vars.mk b/core/clear_vars.mk
index fc6b83c..8488858 100644
--- a/core/clear_vars.mk
+++ b/core/clear_vars.mk
@@ -264,6 +264,7 @@
 LOCAL_UNINSTALLABLE_MODULE:=
 LOCAL_UNSTRIPPED_PATH:=
 LOCAL_USE_AAPT2:=$(USE_AAPT2)
+LOCAL_USE_R8:=
 LOCAL_USE_VNDK:=
 LOCAL_VENDOR_MODULE:=
 LOCAL_VTSC_FLAGS:=