Improve AIX port some more.

Improve AIX port some more.

With this, it should be as good as it was in 23.3, though it's
still pretty bad: the dumped emacs does not run.  See Mark Fleishman in
http://lists.gnu.org/archive/html/help-gnu-emacs/2011-04/msg00287.html
* unexaix.c (start_of_text): Remove.
(_data, _text): Declare as char[], not int, as AIX manual suggests.
(bias, lnnoptr, text_scnptr, data_scnptr, load_scnptr)
(orig_load_scnptr, orig_data_scnptr):
Now off_t, not long, since they are file offsets.
(make_hdr): Use _data, not start_of_data ().
This is the key part of the fix.
(make_hdr, unrelocate_symbols): Use off_t for file offsets.
(unrelocate_symbols): Cast pointers to intptr_t, not to ulong.

Fixes: debbugs:13650