Fix macOS build by including unistd.h in gzguts.h for non-Windows platforms

Co-authored-by: 3dJan <56254096+3dJan@users.noreply.github.com>

Author: Copilot

Libraries/zlib/Include/gzguts.h

@@ -38,6 +38,10 @@
 #  include <io.h>
 #endif
 
+#if !defined(_WIN32)
+#  include <unistd.h>
+#endif
+
 #if defined(_WIN32)
 #  define WIDECHAR
 #endif