Remove unused arguments for unexec.

Remove unused arguments for unexec.
The third one is never used, and the last two are always passed as zero.
* src/emacs.c (unexec): Add declaration.
(Fdump_emacs): Only pass the first two arguments to unexec.
Simplify #ifdef.
* src/unexw32.c (unexec):
* src/unexsol.c (unexec):
* src/unexhp9k800.c (unexec):
* src/unexcw.c (unexec): Remove the last 3 arguments, unused.
* src/unexelf.c (unexec): Remove the last 3 arguments, unused.
(find_section): Use const.
* src/unexmacosx.c (unexec): Remove the last 3 arguments, unused.
(unexec_error): Declare it NO_RETURN.
* src/unexcoff.c (make_hdr): Assume bss_start is always zero, remove
it as an argument, remove data_start and entry_address arguments, unused.
(unexec): Remove bss_start, data_start and
entry_address arguments.
* src/unexaix.c (make_hdr): Assume bss_start is always zero, remove
it as an argument, remove data_start and entry_address arguments, unused.
(unexec): Remove bss_start, data_start and
entry_address arguments.