test: add test that caused gofrontend to crash

Apparently people don't tend to pass untyped constant expressions
to panic.

For #68734

Change-Id: I6fff8137a0f001391de9e61860b67026a9db08c2
Reviewed-on: https://go-review.googlesource.com/c/go/+/603096
Reviewed-by: David Chase <[email protected]>
Auto-Submit: Ian Lance Taylor <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>
Reviewed-by: Ian Lance Taylor <[email protected]>
Commit-Queue: Ian Lance Taylor <[email protected]>

Author: ianlancetaylor

test/fixedbugs/issue68734.go

@@ -0,0 +1,17 @@
+// compile
+
+// Copyright 2024 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// The gofrontend had a bug handling panic of an untyped constant expression.
+
+package issue68734
+
+func F1() {
+	panic(1 + 2)
+}
+
+func F2() {
+	panic("a" + "b")
+}