Do not depend on HAVE_SYSCTL when deciding

Do not depend on HAVE_SYSCTL when deciding
whether to include files.  Include <sys/param.h> if
HAVE_SYS_PARAM_H (not HAVE_SYSCTL).
(main) [defined __POWERPC__]: Add a kludge to work around a
Mac OS X bug, so that uname -p defaults to "powerpc" if
sysctl ((int[]) {CTL_HW, HW_MACHINE_ARCH}, 2, buffer, &bufsize, 0, 0)
fails.  Problem reported by Petter Reinholdtsen in:
http://lists.gnu.org/archive/html/bug-gnu-utils/2003-02/msg00201.html