Build fixes:

- Fixed build error, which was previously introduced by commit
c8ca89112e

- Treat warnings as errors

unittest/libmariadb/my_test.h

@@ -38,6 +38,7 @@ with this program; if not, write to the Free Software Foundation, Inc.,
 #include <pthread.h>
 #else
 #include <io.h>
+#define unlink _unlink
 #endif
 
 #ifndef OK