perf tools: Convert getpagesize() uses to sysconf(_SC_GETPAGESIZE)

Using the more portable and equivalent sysconf call.

Reported-by: Aristeu Rozanski <aris@redhat.com>
Reported-by: Ulrich Drepper <drepper@redhat.com>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Aristeu Rozanski <aris@redhat.com>
Cc: Frédéric Weisbecker <fweisbec@gmail.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Ulrich Drepper <drepper@redhat.com>
LKML-Reference: <1263501006-14185-1-git-send-email-acme@infradead.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>