Include sys/types.h for proper typedefs related to wait()

Should fix #1519

utest/test_fork.c

@@ -32,6 +32,7 @@ USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 **********************************************************************************/
 
 #include "openblas_utest.h"
+#include <sys/types.h>
 #include <sys/wait.h>
 #include <cblas.h>