autotools: include pthread.h when checking for clockid_t/timer_t
autotools: include pthread.h when checking for clockid_t/timer_t

Must include pthread.h to check for clockid_t and timer_t. This is
because MinGW and MinGW-w64 both put the time related definitions
in pthread headers and not in sys/types.h. Without optionally
including pthread.h, the check for these types may mistakenly fail.

git-svn-id: caee63afe878fe2ec7dbba394a86c9654d9110ca@981 64e312b2-a51f-0410-8e61-82d0ca0eb02a

svn2github/check,dashaomai/check-code,svn2github/check,svn2github/check,svn2github/check,dashaomai/check-code,svn2github/check,dashaomai/check-code,dashaomai/check-code