split up process.c [was: Re: Changes in process.c]

[Dan Nicolaescu <dann@gnu.org>]

Eli Zaretskii <eliz@gnu.org> writes:

> People who make changes in process.c related to keyboard input and
> wait_reading_process_output, please remember that there are two
> branches in process.c, one for systems that support async
> subprocesses, the other for those which don't (only MS-DOS in the
> latter class).  Making changes only in one of them is going to break
> something.

This points to the ugliness of the situation.

Why don't we split the part for supporting MS-DOS into a different
file: process-no-subprocesses.c (or some better name)

That makes the file easier to read, less clunky, and problems easier
to catch with a simple grep.