[libcpp] RFA: Add support for comments retrieval

[Paolo Bonzini]

> +typedef struct
> +{
> +  const char *comment;   /* string containing comment at a given location.  */

Should be

  /* Text of the comment including (or is it excluding?) the
     terminators.  */
  const char *comment;

  /* Source location for the given comment.  */
  source_location sloc;

... and likewise for the other struct.

Thanks,

Paolo