remove warning about alreday defined Z_PREFIX

diff --git a/3rdparty/zlib/1.2.8/zconf.h.cmakein b/3rdparty/zlib/1.2.8/zconf.h.cmakein
index 043019cda1db5ec2ca6a7c82acce4d559e9787d0..1f4778b045574d354c9d632bca89d8ec1f37b22c 100644 (file)
--- a/3rdparty/zlib/1.2.8/zconf.h.cmakein
+++ b/3rdparty/zlib/1.2.8/zconf.h.cmakein
@@ -7,7 +7,9 @@
 
 #ifndef ZCONF_H
 #define ZCONF_H
+#ifndef Z_PREFIX
 #cmakedefine Z_PREFIX
+#endif
 #cmakedefine Z_HAVE_UNISTD_H
 
 /*