Fix MinGW make error 'MSG_NOSIGNAL' undeclared (closes #175)

Thank you Marjan Tomas.

tests/unit-test-server.c

@@ -27,6 +27,11 @@
 # include <sys/socket.h>
 #endif
 
+/* For MinGW */
+#ifndef MSG_NOSIGNAL
+# define MSG_NOSIGNAL 0
+#endif
+
 #include "unit-test.h"
 
 enum {