NoMallocThreadPool: include pthread if using pthread (#417)

Using clang with libc++ does not include pthread.h implicitly through
<thread> by default, so using pthread_t will cause a compilation error.

Signed-off-by: Christopher Degawa <ccom@randomderp.com>

source/Lib/Utilities/NoMallocThreadPool.h

@@ -52,6 +52,10 @@ POSSIBILITY OF SUCH DAMAGE.
 #include <chrono>
 #include <array>
 
+#ifdef HAVE_PTHREADS
+#include <pthread.h>
+#endif
+
 #include "CommonLib/CommonDef.h"
 #if ENABLE_TIME_PROFILING_MT_MODE
 #include "CommonLib/TimeProfiler.h"