add new make target "all", to build all known targets



git-svn-id: http://skia.googlecode.com/svn/trunk@237 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/Makefile b/Makefile
index cce996a..4decd28 100644
--- a/Makefile
+++ b/Makefile
@@ -144,6 +144,9 @@
 
 ##############################################################################
 
+.PHONY: all
+all: $ bench gm skimage tests
+
 .PHONY: clean
 clean:
 	$(HIDE)rm -rf out