While a typedef can be specified in message files for the messages following
with the `MessageIdTypedef` directive, only the last typedef was honored by
windmc. This corrects this behavior, matching mc.exe functionality.
* windmc.h (struct mc_node): Add id_typecast field.
* mcparse.y (message): Initialise the id_typecast field.
* windmc.c (write_dbg): Use the id_typecast field as a parameter
when calling write_dbg_define.
(write_header): Likewise.