Clean up <sys/types.h>

[H.J. Lu]

I think <sys/types.h> defines too many symbols and it gets included
unconditionally in too many header files. It should be cleaned up.
For each header file, which include <sys/types.h>, it should do
something like

#define __get_sys_types
#define __need_this_type
#include <sys/types.h>

<sys/types.h> should check both __get_sys_types and __need_this_type.


-- 
H.J. Lu (hjl@gnu.org)