[csplit] Move assert() support function to shared libraries.

[csplit] Move assert() support function to shared libraries.

Three versions are implemented:
 * __stdc_assert() in stdc.library that uses a requester.
 * __stdcdos_assert() in stdcio.library that uses that library's I/O functions.
 * __nixc_assert() in posixc.library that uses that library's I/O functions.
 * delint by Jason S. McMullan

git-svn-id: https://svn.aros.org/svn/aros/trunk@48050 fb15a70f-31f2-0310-bbcc-cdcc74a49acc