Solve some Windows build issues.

* main.c (main): Use ONS(), not OSN().
(prepare_mutex_handle_string) [WINDOWS32]: Use %Ix formatting to
support both 32bit and 64bit systems.
* job.c (free_child, new_job): Use ONS(), not OSN().
* w32/subproc/w32err.c (map_windws32_error_to_string): Use O() when
calling fatal().

Copyright-paperwork-exempt: yes
* main.c (decode_env_switches): Ensure we have enough space.

Reported (with patch) by Gerte Hoogewerf <g.hoogewerf@gmail.com>
* w32/*: Remove TABs from the source code.

I know whitespace commits are annoying, but having these TABs is
causing me to miss things when I search through the code.  This
doesn't try to change the w32 code to meet GNU coding standards.