perf tools: Fix the NO_64BIT build on pure 64-bit systems

Randy Dunlap reported that 'make NO_64BIT=1' fails to build
a pure 32-b it binary on 64-bit/64-bit x86 systems.

The reason is that we dont pass in the -m32 and GCC defaults
to -m64.

So pass it in - and also extend the warning message about libelf
dependencies - glibc-dev[el] is needed as well beyond the libelf
library.

Reported-by: Randy Dunlap <randy.dunlap@oracle.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
LKML-Reference: Message-Id: <20091005131729.78444bfb.randy.dunlap@oracle.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>