try to fix openbsd build

git-svn-id: http://svn.freeswitch.org/svn/freeswitch/trunk@10379 d0543943-73ff-0310-b7d9-9358b9ac24b2

src/include/switch_apr.h

@@ -44,6 +44,7 @@ SWITCH_BEGIN_EXTERN_C
 #ifdef WIN32
 typedef HANDLE                switch_thread_id_t;
 #else
+#include <pthread.h>
 typedef pthread_t             switch_thread_id_t;
 #endif