cmd/compile: "F is not a generic type" when F is a recursive generic interface

On tip (e9e0d1ef70) with `-gcflags=-G=3`

Repro:
```
package p

type F[t F[t]] interface {}
```

Compiler rejects it with:

```
go build -gcflags=-G=3 j.go
# command-line-arguments
./j.go:3:10: F is not a generic type
```

However, it accepts this:

```
package p

type F[t F] interface {}
```

But that has other problems, see #47837.
