What should be in <sys/param.h>?

[Roland McGrath]

<sys/param.h> only exists for compatibility with old applications that have
usage predating the better ways now available to get such information.  So
all that matters is that it has what was there in the past when that
application could be compiled on that platform.  If you are compiling a
program someplace it was never compiled in the past, then you should fix it
to use the modern interfaces.