[Win32] Use `exit` instead of `type` [ci skip]

`exit` command ignores the rest arguments after an exit code, while
`type` command tries to read all as files.

win32/Makefile.sub

@@ -4,7 +4,7 @@ SHELL = $(COMSPEC)
 ECHO1 = $(V:1=@:)
 RUNCMD = $(COMSPEC) /c
 MKFILES = Makefile verconf.mk
-NULLCMD = type nul
+NULLCMD = exit /b0.		# exit ignores the rest
 NULL = nul
 CHDIR = cd
 PATH_SEPARATOR = ;