mkfiles: fix macargv buf

R=rsc
http://codereview.appspot.com/2729042

src/cmd/devdraw/mkfile

@@ -46,3 +46,5 @@ install-macargv: $O.macargv
 
 $O.macargv: macargv.$O
 	$LD -o $target $prereq
+
+install: $MACARGV

src/cmd/devdraw/mkwsysrules.sh

@@ -52,7 +52,7 @@ elif [ $WSYSTYPE = osx ]; then
 		echo 'LDFLAGS=$LDFLAGS -F/System/Library/PrivateFrameworks'
 	fi
 	echo 'WSYSOFILES=$WSYSOFILES osx-screen-carbon-objc.o osx-draw.o osx-srv.o'
-	echo 'install: install-macargv'
+	echo 'MACARGV=install-macargv'
 elif [ $WSYSTYPE = nowsys ]; then
 	echo 'WSYSOFILES=nowsys.o'
 fi

src/cmd/rio/mkfile

@@ -40,7 +40,3 @@ error.$O: showevent/ShowEvent.c
 
 $O.xshove: xshove.$O
 	$LD -o $O.xshove xshove.$O -lX11
-
-# bug in reusing mksysrules.sh
-install-macargv:
-	true