Added explicit 'void' to function that takes no argument

This is the correct way to tell that a function takes no
arguments, because an empty parameter list tells the compiler
that it is not yet defined, and is tolerated only for
compatibility with very old C compilers for whom prototypes
were not yet a defined language element.

util/wxcopy.c

@@ -33,7 +33,7 @@
 
 extern char *__progname;
 
-void print_help()
+void print_help(void)
 {
 	printf("Usage: %s [OPTIONS] [FILE]\n", __progname);
 	puts("Copies data from FILE or stdin into X cut buffer.");