sys/types.h header file Issue

[Channa <channa.kad%gmail.com@localhost>]

Hi,

I am using NetBSD sources have some doubt with respect to the
 <pthread_types.h> inclusion in <sys/types.h> header file.

The header file <pthread_types.h> is included as below:

$ cat src/sys/sys/types.h
:
:
#if (_POSIX_C_SOURCE - 0L) >= 199506L || (_XOPEN_SOURCE - 0) >= 500 || \
    defined(_NETBSD_SOURCE)
#include <pthread_types.h>
#endif
:

What is the reason for including <pthread_types.h> under the macros
'_POSIX_C_SOURCE'
or '_XOPEN_SOURCE' ?

Since the IEEE specification for <sys/types.h> below does not mention
such a rule

http://www.opengroup.org/onlinepubs/000095399/basedefs/sys/types.h.html#tag_13_67

Is it ok to move the inclusion of <pthread_types.h> outside these macros?

Thanks & Regards,
Channa