fix windows Make.cmd:

- TARG had extra space at the end;
- it should be set before "all" target.

R=rsc, Joe Poirier
CC=golang-dev
https://golang.org/cl/1846042

src/Make.cmd

@@ -2,6 +2,10 @@
 # Use of this source code is governed by a BSD-style
 # license that can be found in the LICENSE file.
 
+ifeq ($(GOOS),windows)
+TARG:=$(TARG).exe
+endif
+
 all: $(TARG)
 
 # ugly hack to deal with whitespaces in $GOROOT
@@ -11,10 +15,6 @@ QUOTED_GOROOT:=$(subst $(space),\ ,$(GOROOT))
 
 include $(QUOTED_GOROOT)/src/Make.common
 
-ifeq ($(GOOS),windows) 
-TARG:=$(TARG).exe 
-endif
-
 PREREQ+=$(patsubst %,%.make,$(DEPS))
 
 $(TARG): _go_.$O $(OFILES)