Move directive handling into the lexer itself.

Move directive handling into the lexer itself.

        * cpplex.c (_cpp_lex_token): Handle directives directly.
        In the case of a directive interrupting a function-like
        macro invocation, use extra_char since read_ahead is
        used to store the '#'.  Return a CPP_EOF in this case.
        * cppmacro.c (parse_arg): No need to handle CPP_DHASH any more.
        (cpp_get_token): Don't handle directives here.
        * cpplib.h: Remove CPP_DHASH token type.

From-SVN: r37329