Now install sadc in $prefix/lib64 directory on 64 bit machines

Now install sadc in $prefix/lib64 directory on 64 bit machines
even if $prefix/lib also exists.

$prefix/lib no longer takes precedence on $prefix/lib64 directory
if this latter exists on 64 bit machines.
CPU is 64 bit if it has the lm (long mode) flag in /proc/cpuinfo.

Mail from Wayne Lin <wlin@mvista.com> 14/11/2012:
Subject: why 64 bit sa1 sa2 sadc are in /usr/lib and not in /usr/lib64?

We like the sysstat package, we are just curious why by default when built
on 64 bit system and targeting 64 bit system, the /sa and its content
sa1, sa2, sadc are being put in /usr/lib and not /usr/lib64?
Should we just use sa_lib_dir to configure the redirect?