MDEV-5120 Test suite test maria-no-logging fails

stat structure (from <sys/stat.h>) is conditionally defined
to have different layout and size depending on the defined macros.
The correct macro is defined in my_config.h, which means it MUST be
included first (or, at least before <features.h> - so, practically,
before including any system headers).

plugin/handler_socket/libhsclient/socket.cpp

@@ -6,6 +6,8 @@
  * See COPYRIGHT.txt for details.
  */
 
+#include <my_config.h>
+
 #include <stdexcept>
 #include <string.h>
 #include <errno.h>