cmake: Include time.h on several checks to prevent false negatives

cmake: Include time.h on several checks to prevent false negatives

The clock_t, clockid_t and timer_t types are deemed not found when they
are actually available if time.h is included. Include the header during
the checks.

Patch#53

git-svn-id: svn+ssh://svn.code.sf.net/p/check/code/trunk@1204 64e312b2-a51f-0410-8e61-82d0ca0eb02a