[XLScc] Issue adding ac_complex

While adding ac_complex I ran across one road block.
Using the following simple test:

```
#include "xls_int.h"
#include "ac_compat/ac_complex.h"

long long my_package() {
ac_datatypes::ac_complex> bx(1);
return bx.r();
}
```

Where the function r() from ac_type/ac_complex.h is defined as:
T &r() { return _r; }

I get the following error:
```
UNIMPLEMENTED: Don't know how to translate lvalue of type MemberExpr from callee context
78 --> /tmp/xls_tempfile_pAHgml.cc:9:14
79 |
80 9 | return bx.r();
81 |
```