clib2 Code

- Added the POSIX exec() family functions, based upon code contributed
by Henning Nielsen Lund. Thank you very much!

- atoll() no longer sets 'errno' directly but now calls __set_errno()
instead.

- Fixed to compile correctly.

- Changed how multi-volume assignments are handled by execve().

- The types of the __default_path_delimiter and __default_path variables
were wrong.

- Rewrote execve() from scratch and documented it.

- The default configuration options for execvp() are now configurable at
link time.

- Added the exec() family functions to the makefiles and the <unistd.h>
header file.

- Added preliminary versions of the exec() family functions.

- Added the missing string pointer.

- Added pathconf() and fpathconf() as contributed by Peter Bengtsson. Thank you very much!

- Added sysinfo() as contributed by Peter Bengtsson. Thank you very much!