Fix compilation with --solo and --debug combined.

However this ends up not really being solo, since it has to
include external libraries.

zutil.c

@@ -113,7 +113,7 @@ uLong ZEXPORT zlibCompileFlags()
 }
 
 #ifdef ZLIB_DEBUG
-
+#include <stdlib.h>
 #  ifndef verbose
 #    define verbose 0
 #  endif