code review 4082047: cgo: improve error reporting slightly.

src/cmd/cgo/main.go

 // Copyright 2009 The Go Authors.  All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
 // Cgo; see gmp.go for an overview.
 
 // TODO(rsc):
 //      Emit correct line number annotations.
 //      Make 6g understand the annotations.
 
@@ skipping 80 matching lines @@
 }
 
 // A FuncType collects information about a function type in both the C and Go worlds.
 type FuncType struct {
         Params []*Type
         Result *Type
         Go     *ast.FuncType
 }
 
 func usage() {
-        fmt.Fprint(os.Stderr, "usage: cgo [compiler options] file.go ...\n")
+        fmt.Fprint(os.Stderr, "usage: cgo -- [compiler options] file.go ...\n")
+        flag.PrintDefaults()
         os.Exit(2)
 }
 
 var ptrSizeMap = map[string]int64{
         "386":   4,
         "amd64": 8,
         "arm":   4,
 }
 
 var cPrefix string
@@ skipping 136 matching lines @@
                                 p.Name[k] = v
                         } else if !reflect.DeepEqual(p.Name[k], v) {
                                 error(token.NoPos, "inconsistent definitions for C.%s", k)
                         }
                 }
         }
 
         p.ExpFunc = append(p.ExpFunc, f.ExpFunc...)
         p.Decl = append(p.Decl, f.AST.Decls...)
 }