perf tools, x86: Fix 32-bit compile on 64-bit system

Builds for 32-bit perf binaries on a 64-bit host currently fail
with this error:

 [...]
 bench/../../../arch/x86/lib/memcpy_64.S: Assembler messages:
 bench/../../../arch/x86/lib/memcpy_64.S:29: Error: bad register name `%rdi'
 bench/../../../arch/x86/lib/memcpy_64.S:34: Error: invalid instruction suffix for `movs'
 bench/../../../arch/x86/lib/memcpy_64.S:50: Error: bad register name `%rdi'
 bench/../../../arch/x86/lib/memcpy_64.S:61: Error: bad register name `%rdi'
 ...

The problem is the detection of the host arch without considering passed in
flags. This change fixes 32-bit builds via:

make EXTRA_CFLAGS=-m32

and 64-bit builds still reference the memcpy_64.S.

Signed-off-by: David Ahern <dsahern@gmail.com>
Acked-by: Frederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: <stable@kernel.org>
Link: http://lkml.kernel.org/r/1310420304-21452-1-git-send-email-dsahern@gmail.com
Signed-off-by: Ingo Molnar <mingo@elte.hu>