re-enable "core" build target lost in r1968

git-svn-id: http://skia.googlecode.com/svn/trunk@1970 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/Makefile b/Makefile
index aee6efd..f5fa963 100644
--- a/Makefile
+++ b/Makefile
@@ -29,7 +29,7 @@
 
 BUILDTYPE ?= Debug
 CWD := $(shell pwd)
-ALL_TARGETS := SampleApp bench gm tests tools
+ALL_TARGETS := core SampleApp bench gm tests tools
 
 # Default target.  This must be listed before all other targets.
 .PHONY: default