c++ add rid entries for choose_expr and types_compatible_p

[Neil Booth]

Aldy Hernandez wrote:-

> from cp/lex.c and c-parse.in:
> 
>     /* Table mapping from RID_* constants to yacc token numbers.
>        Unfortunately we have to have entries for all the keywords in all
>        three languages.  */

And yet they are maintained separately.  It would be nice to find a
way of putting this stuff in one place; I don't believe it is impossible.

Neil.