Adapt to new location of libcore

Change-Id: Ibabfe907f00522c1966ddc333352eaea2bdcb5bd
diff --git a/core/main.mk b/core/main.mk
index 043fef5..91b952b 100644
--- a/core/main.mk
+++ b/core/main.mk
@@ -400,7 +400,7 @@
 subdirs += \
 	build/tools/signapk \
 	dalvik/dx \
-	dalvik/libcore \
+	libcore \
 	sdk/archquery \
 	sdk/androidprefs \
 	sdk/apkbuilder \