Initial implementation of an async DNS client API with getaddrinfo + pthreads.

src/system.h

@@ -113,11 +113,13 @@
 #define uhub_assert assert
 
 #ifdef __linux__
+#define POSIX_THREAD_SUPPORT
 #define USE_EPOLL
 #include <sys/epoll.h>
 #endif
 
 #ifdef BSD_LIKE
+#define POSIX_THREAD_SUPPORT
 /*
 #define USE_KQUEUE
 #include <sys/event.h>
@@ -279,6 +281,10 @@ typedef unsigned __int64 uint64_t;
 #define NEED_GETOPT
 #endif
 
+#ifdef POSIX_THREAD_SUPPORT
+#include <pthread.h>
+#endif
+
 #if defined(__CYGWIN__) || defined(__MINGW32__) || defined(_MSC_VER)
 #define PLUGIN_API __declspec(dllexport)
 #else