cmd/dist: pass -Wno-unknown-warning-option in swig_callback_lto

For #46557
Fixes #46991

Change-Id: Ic88ebaa13d3edf904657dc19ada4fd4ff7f44a8f
Reviewed-on: https://go-review.googlesource.com/c/go/+/332010
Trust: Ian Lance Taylor <iant@golang.org>
Trust: Josh Bleecher Snyder <josharian@gmail.com>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Josh Bleecher Snyder <josharian@gmail.com>

Author: ianlancetaylor

src/cmd/dist/test.go

@@ -737,9 +737,9 @@ func (t *tester) registerTests() {
 						fn: func(dt *distTest) error {
 							cmd := t.addCmd(dt, "misc/swig/callback", t.goTest())
 							cmd.Env = append(os.Environ(),
-								"CGO_CFLAGS=-flto -Wno-lto-type-mismatch",
-								"CGO_CXXFLAGS=-flto -Wno-lto-type-mismatch",
-								"CGO_LDFLAGS=-flto -Wno-lto-type-mismatch",
+								"CGO_CFLAGS=-flto -Wno-lto-type-mismatch -Wno-unknown-warning-option",
+								"CGO_CXXFLAGS=-flto -Wno-lto-type-mismatch -Wno-unknown-warning-option",
+								"CGO_LDFLAGS=-flto -Wno-lto-type-mismatch -Wno-unknown-warning-option",
 							)
 							return nil
 						},