Do not look for zconf.h in the source directory.

Temporary patch for cmake, but too violent. A better solution will
need to be found.

Author: Vollstrecker

zlib.h

@@ -31,7 +31,7 @@
 #ifndef ZLIB_H
 #define ZLIB_H
 
-#include "zconf.h"
+#include <zconf.h>
 
 #ifdef __cplusplus
 extern "C" {