Issue with pointers in exprparser
```c
#define STREAMPROC_DUMMY               (STREAMPROC*)0
```
Outputs
```nim
const
  STREAMPROC_DUMMY* = cast[STREAMPROC*](0)
```
Should generate
```nim
const
  STREAMPROC_DUMMY* = cast[ptr STREAMPROC](0)
```

cc: @jyapayne 