Enable D8 by default.

Bug: 67569208
Test: m -j32

Change-Id: Ie80ce7ca0e6955ef6c1fbae1fa5b169374068cf4
diff --git a/core/config.mk b/core/config.mk
index 566faae..ccd7663 100644
--- a/core/config.mk
+++ b/core/config.mk
@@ -512,7 +512,7 @@
 USE_PREBUILT_SDK_TOOLS_IN_PLACE := true
 
 # USE_D8_BY_DEFAULT is the default behavior, use USE_D8 to override.
-USE_D8_BY_DEFAULT := false
+USE_D8_BY_DEFAULT := true
 ifndef USE_D8
   USE_D8 := $(USE_D8_BY_DEFAULT)
 endif