nuttx: Add missing pthread.h header (#2009)

core/shared/platform/nuttx/platform_internal.h

@@ -14,6 +14,7 @@
 #include <inttypes.h>
 #include <limits.h>
 #include <poll.h>
+#include <pthread.h>
 #include <stdarg.h>
 #include <stdbool.h>
 #include <stdio.h>