Allow sdk/builders to be built using Windows SDK.

Change-Id: Ic3c8bc2bace166442bf780b625e5d528fea4df9f
diff --git a/core/main.mk b/core/main.mk
index f0ef602..3de1b20 100644
--- a/core/main.mk
+++ b/core/main.mk
@@ -399,6 +399,7 @@
 	sdk/layoutlib_utils \
 	sdk/ninepatch \
 	sdk/sdkstats \
+	sdk/builders \
 	sdk/sdkmanager \
 	sdk/layoutopt \
 	development/apps \