Convert maybe_fatal to standard C.

Convert maybe_fatal to standard C.
* src/lisp.h (verror): Declare.
* src/eval.c (verror): New function containing the code from ...
(error): ... this.  Call verror.
* src/term.c (vfatal): New function containing the code from ...
(fatal): ... this.  Call vfatal.
(maybe_fatal): Convert to standard C, use variable number of
arguments.  Declare as non-return.
(init_tty): Fix maybe_fatal call.