cmd/compile: fix fmt_test (fix long test build)

Follow-up on https://golang.org/cl/146782.

TBR=bradfitz

Change-Id: Idaf5488fedfc05d6ff71706fa0bcd70bf98ab25a
Reviewed-on: https://go-review.googlesource.com/c/147283Reviewed-by: Robert Griesemer <gri@golang.org>

src/cmd/compile/fmt_test.go

@@ -587,6 +587,7 @@ var knownFormats = map[string]string{
 	"*cmd/compile/internal/types.Sym %S":              "",
 	"*cmd/compile/internal/types.Sym %p":              "",
 	"*cmd/compile/internal/types.Sym %v":              "",
+	"*cmd/compile/internal/types.Type %#L":            "",
 	"*cmd/compile/internal/types.Type %#v":            "",
 	"*cmd/compile/internal/types.Type %+v":            "",
 	"*cmd/compile/internal/types.Type %-S":            "",