Add device abstraction code for the UEFI Console and UEFI Shell-based file systems.

Add device abstraction code for the UEFI Console and UEFI Shell-based file systems.
Make argv use narrow characters instead of wide characters.
Add setenv functionality.
Add poll() system call.
Change signal names into macros – required for standards compliance.  The enums were renamed and moved to sys/signal.h and the new macros reference the enums.
Added SIGBREAK, which is required for Python.
Modify stdio functions to fail cleanly when called with a NULL File Pointer argument.
Added <sys/cdefs.h> that just includes <sys/EfiCdefs.h>.  By adding this wrapper, we improve compatibility with *nix files which assume <sys/cdefs> exists.
Add <netdb.h>
Added macros for bcopy(), bcmp() and strsep().
Modify the clock() function so that it does not hang when running under an emulation environment such as NT32.
Move TM structure specific macros from the private tzfile.h into <time.h>
Add strncasecmp function.
Add strptime function.
Add gettimeofday function.
Add getcwd function.

git-svn-id: https://edk2.svn.sourceforge.net/svnroot/edk2/trunk/edk2@11908 6f19259b-4bc3-4df7-8a09-765794883524