configure: PTHREADS should be defined on cygwin, as well

Signed-off-by: Jon TURNEY <jon.turney@dronecode.org.uk>
Signed-off-by: Brian Paul <brianp@vmware.com>

(cherry picked from commit c1a4f249f18a766488da0832fbf6700de93af2f8)
1 file changed