perf trace/scripting: Fix compile error when libperl not installed

When I added the xs callbacks into perf, I forgot to re-check
the no-libperl case. This patch fixes the undefined reference
error for that.

Reported-by: Arnaldo Carvalho de Melo <acme@ghostprotocols.net>
Signed-off-by: Tom Zanussi <tzanussi@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
LKML-Reference: <1260153712.6564.4.camel@tropicana>
Signed-off-by: Ingo Molnar <mingo@elte.hu>