with GCC, the compiler does not stumble over `size_t', `ptrdiff_t',
and `wchar_t'. Also note that the comment in <stddef.h> says that we
have to #include <sys/stdtypes.h> before including <stddef.h> when on
a sun.
command line option.
* listing.h, listing.c: now prints addresses with ??? instead of 0 when
errors in assemble prevent addresses being known. Prints
symbol table more tidily. Allows different parts of the
listing to be selected.
