cmd/compile: update TestFormats for CL 196959

CL 196959 uses %v to print *EscLocation values. This happens at least at
    Fatalf("path inconsistency: %v != %v", edge.src, src)
in (*Escape).explainPath.

Change-Id: I1c761406af6a1025403dfefa5ec40aee75e72944
Reviewed-on: https://go-review.googlesource.com/c/go/+/205377
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/cmd/compile/fmtmap_test.go

@@ -21,6 +21,7 @@ package main_test
 // An empty new format means that the format should remain unchanged.
 var knownFormats = map[string]string{
 	"*bytes.Buffer %s":                                "",
+	"*cmd/compile/internal/gc.EscLocation %v":         "",
 	"*cmd/compile/internal/gc.Mpflt %v":               "",
 	"*cmd/compile/internal/gc.Mpint %v":               "",
 	"*cmd/compile/internal/gc.Node %#v":               "",