go/build: make compatible with go/build

The irony!

R=golang-dev, r
CC=golang-dev
https://golang.org/cl/5482062

src/pkg/go/build/Makefile

@@ -11,7 +11,7 @@ GOFILES=\
 	path.go\
 	syslist.go\
 
-CLEANFILES+=syslist.go pkgtest/_obj cmdtest/_obj cgotest/_obj
+CLEANFILES+=pkgtest/_obj cmdtest/_obj cgotest/_obj
 
 include ../../../Make.pkg
 

src/pkg/go/build/syslist.go

+// Generated automatically by make.
+package build
+
+const goosList = "darwin freebsd linux netbsd openbsd plan9 windows "
+const goarchList = "386 amd64 arm "