runtime: fix file reference in comments

cmd/compile/internal/ld/decodesym.go is now
cmd/link/internal/ld/decodesym.go

Change-Id: I16ec5c89aa3507e70676c2b50d70f1fde533a085
Reviewed-on: https://go-review.googlesource.com/44373Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/runtime/type.go

@@ -22,7 +22,7 @@ const (
 	tflagNamed     tflag = 1 << 2
 )
 
-// Needs to be in sync with ../cmd/compile/internal/ld/decodesym.go:/^func.commonsize,
+// Needs to be in sync with ../cmd/link/internal/ld/decodesym.go:/^func.commonsize,
 // ../cmd/compile/internal/gc/reflect.go:/^func.dcommontype and
 // ../reflect/type.go:/^type.rtype.
 type _type struct {