[csplit] Added frame for stdc.library, stdcio.library and posixc.library

[csplit] Added frame for stdc.library, stdcio.library and posixc.library

 * Reserved LVOs for all of the function to be part of these libraries.
 * Added commented out .alias lines for functions where appropriate
 * Added open tests
 * Adapted gcc compiler default link libraries.
 * Provide background autodocs.
 * stdc.static implementation based on code from Jason S. McMullan
 * stdc.library should only depend on exec.library. Provide support code
   in __optionallibs.[ch] to check if functions of certain library may
   be called.

git-svn-id: https://svn.aros.org/svn/aros/trunk@48029 fb15a70f-31f2-0310-bbcc-cdcc74a49acc