makekeys: Detach ourselves from X headers entirely

Subsequent to a121b7b0 we are no longer building makekeys with enough -I/foo/bar to find the X11 headers, so if they're not in a system include path, things fail. Since this utility is only needed at build time, there's no real reason to demand the X headers be installed for both the build and target machines if cross- compiling, we can just assume a vaguely ANSI environment instead.

Reported-by: Zeising on #xorg-devel Reviewed-by: Keith Packard keithp@keithp.com