cmd/cgo: don't track same node twice in guessKinds

Change-Id: Ib2c1490a42e3485913a05a0b2fecdcc425d42871
Reviewed-on: https://go-review.googlesource.com/36083
Run-TryBot: Ian Lance Taylor <[email protected]>
TryBot-Result: Gobot Gobot <[email protected]>
Reviewed-by: Ian Lance Taylor <[email protected]>

Author: hirochachacha

src/cmd/cgo/gcc.go

@@ -269,11 +269,10 @@ func (p *Package) guessKinds(f *File) []*Name {
 			}
 		}
 
-		needType = append(needType, n)
-
 		// If this is a struct, union, or enum type name, no need to guess the kind.
 		if strings.HasPrefix(n.C, "struct ") || strings.HasPrefix(n.C, "union ") || strings.HasPrefix(n.C, "enum ") {
 			n.Kind = "type"
+			needType = append(needType, n)
 			continue
 		}