perf_counter: tools: Makefile tweaks for 64-bit powerpc

On 64-bit powerpc, perf needs to be built as a 64-bit executable.
This arranges to add the -m64 flag to CFLAGS if we are running on
a 64-bit machine, indicated by the result of uname -m ending in "64".
This means that we'll use -m64 on x86_64 machines as well.

Signed-off-by: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: linuxppc-dev@ozlabs.org
Cc: benh@kernel.crashing.org
LKML-Reference: <19000.55666.866148.559620@cargo.ozlabs.ibm.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>