get_bmask_cmt

get bitmask comment (only for bitfields)
     enum_id - id of enum
     bmask   - bitmask of the constant
     repeatable - type of comment, 0-regular, 1-repeatable
returns: comment attached to bitmask if it exists.
         otherwise returns 0.

long get_bmask_cmt(long enum_id, long bmask, long repeatable);