exp/terminal: fix build on non-Linux using Makefiles

The Makefiles will go away soon.

R=agl
CC=golang-dev
https://golang.org/cl/5544081

src/pkg/exp/terminal/Makefile

@@ -8,7 +8,7 @@ TARG=exp/terminal
 GOFILES=\
 	terminal.go\
 
-ifneq ($(GOOS),windows)
+ifeq ($(GOOS),linux)
 GOFILES+=\
 	util.go
 endif