test: revise testcase for new gccgo compiler bug

Add to the testcase originally created for issue 34577 so
as to also trigger the error condition for issue 34852 (the
two bugs are closely related).

Updates #34577.
Updates #34852.

Change-Id: I2347369652ce500184347606b2bb3e76d802b204
Reviewed-on: https://go-review.googlesource.com/c/go/+/201017
Run-TryBot: Than McIntosh <thanm@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

test/fixedbugs/issue34577.dir/a.go

@@ -8,6 +8,19 @@ type A struct {
 	x int
 }
 
+type AI interface {
+	bar()
+}
+
+type AC int
+
+func (ab AC) bar() {
+}
+
+const (
+	ACC = AC(101)
+)
+
 //go:noinline
 func W(a A, k, v interface{}) A {
 	return A{3}

test/fixedbugs/issue34577.dir/b.go

@@ -17,3 +17,7 @@ func (b B) Func(x a.A) a.A {
 type ktype int
 
 const k ktype = 0
+
+func Func2() a.AI {
+	return a.ACC
+}