Add ro.treble.enabled

Allow users to determine PRODUCT_FULL_TREBLE at runtime.

Bug: 36814984
Test: m -j sailfish and getprop ro.treble.enabled
Change-Id: I58515b1b3742062ae49358ed32bb02a5977e865d
diff --git a/core/main.mk b/core/main.mk
index cc8d665..f51070b 100644
--- a/core/main.mk
+++ b/core/main.mk
@@ -333,6 +333,8 @@
   ADDITIONAL_BUILD_PROPERTIES += ro.bionic.ld.warning=1
 endif
 
+ADDITIONAL_BUILD_PROPERTIES += ro.treble.enabled=${PRODUCT_FULL_TREBLE}
+
 # -----------------------------------------------------------------
 ###
 ### In this section we set up the things that are different