Fix for MINGW32 and clang on windows (#352) (#357)

* Update IXSocket.h

Avoid "conflicting declaration 'typedef SSIZE_T ssize_t'"

* Update IXUdpSocket.h

* Update IXNetSystem.cpp

ENOSPC and EAFNOSUPPORT are not defined for clang on windows

ixwebsocket/IXNetSystem.cpp

@@ -8,6 +8,12 @@
 #include <cstdint>
 #include <cstdio>
 #ifdef _WIN32
+#ifndef EAFNOSUPPORT
+  #define EAFNOSUPPORT 102
+#endif
+#ifndef ENOSPC
+  #define ENOSPC 28
+#endif
 #include <vector>
 #endif