Enable R8 by default (third attempt)

Test: m -j PRODUCT-aosp_x86-userdebug
Test: Check that some .vdex files built have R8 generated code
Change-Id: I5ab4ed75493404c1b330827fe0005510f5613a68
diff --git a/core/config.mk b/core/config.mk
index d317bd0..c54d119 100644
--- a/core/config.mk
+++ b/core/config.mk
@@ -547,7 +547,7 @@
 
 # Default R8 behavior when USE_R8 is not specified.
 ifndef USE_R8
-  USE_R8 := false
+  USE_R8 := true
 endif
 
 #