StdLib: Add directory access functions to PosixLib.

StdLib: Add directory access functions to PosixLib.

Update <dirent.h> and <sys/dirent.h> to latest version.
Enable the tempnam function.
Fix assignments within predicate expressions so that it is clear where assignment is intended and where comparison occurs.
Remove internal.h and DirFunctions.c with its non-portable opendir, closedir, and readdir functions.
Add modified versions of the NetBSD opendir, closedir, and readdir functions.
Fix the declaration of stat() to be standards compliant and consistent with code.

Clean up indentation and declarations of non-existent objects.

Signed-off-by: darylm503
Reviewed-by: lgrosenb
Reviewed-by: lpleahy
Reviewed-by: jljusten
git-svn-id: https://edk2.svn.sourceforge.net/svnroot/edk2/trunk/edk2@12649 6f19259b-4bc3-4df7-8a09-765794883524