std: fix calls to Printf(s) with non-constant s

In all cases the intent was not to interpret s as a format string.
In one case (go/types), this was a latent bug in production.
(These were uncovered by a new check in vet's printf analyzer.)

Updates #60529

Change-Id: I3e17af7e589be9aec1580783a1b1011c52ec494b
Reviewed-on: https://go-review.googlesource.com/c/go/+/587855
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Russ Cox <rsc@golang.org>

src/internal/coverage/cfile/emitdata_test.go

@@ -197,7 +197,7 @@ func testForSpecificFunctions(t *testing.T, dir string, want []string, avoid []s
 		}
 	}
 	if rval != "" {
-		t.Logf("=-= begin output:\n" + output + "\n=-= end output\n")
+		t.Logf("=-= begin output:\n%s\n=-= end output\n", output)
 	}
 	return rval
 }