Skip MacroDefinition output when we don't lex all tokens

Some macro definitions were slipping through here.  E.g., 

```c
#define AV_CH_WIDE_LEFT UINT64_C(0x0000000080000000)
```
was output as 
```julia
const AV_CH_WIDE_LEFT=UINT64_C
```

A better fix would probably be to parse and understand the macro, but that's probably a little ways off...