compiler: support all kinds of recursive types

Previously we only supported recursive types in structs. But there can
be other kinds of recursive types, like slices:

    type RecursiveSlice []RecursiveSlice

This doesn't involve structs, so it led to infinite recursion in the
compiler. This fix avoids recursion at the proper level: at the place
where the named type is defined.

testdata/slice.txt

@@ -16,3 +16,4 @@ bytes: len=6 cap=6 data: 1 2 3 102 111 111
 slice to array pointer: 1 -2 20 4
 unsafe.Add array: 1 5 8 4
 unsafe.Slice array: 3 3 9 15 4
+len: 0