clib2 Code

- Added a description of the thread-safe stdin/stdout/stderr behaviour.

- Activated the dormant thread-safe standard input/output/error
handling code.

- The thread-safe system() call now blocks all standard I/O operations
until the function has returned. Which is harsh, but there is no
elegant solution to the issue of keeping the same dos.library
file handles from concurrent use which SystemTagList() might just
end up using.

- Moved stdlib_main.o into the regular lib.c, at least for
the 68k build. The PowerPC build may follow later, provided
I manage to get the specs file fixed.

- Moved the check for the presence of an FPU into the
math_init.c code.

- Fixed the constructor/destructor invocation sequence for the SAS/C and
GCC 68k library builds.

- Modified the SAS/C constructor/destructor invocation sequence, now that
the names of the functions assigned through the new macros are different.

- Turns out that the constructor/destructor calling sequence
was still wrongish for the OS4 library. So I had to change
it *again*. Which probably means that the 68k library will
need further changes...

- assertion failures early on during program initialization
should no longer spell big trouble on account of the stdio
data structures possibly not being in a well-defined and
initialized state.

- Moved the call chain printing out of stdlib_main.c and into
separate files.

- Removed some more redundant data from stdlib_main.c.

- Added the first real C99 function: _Exit().

- Reorganized the local header files, removing redundancies.

- Dropped unused stub code which is now redundant because of
the constructor/destructor mechanism.