perf bench mem: Ignore export.h related changes to mem{cpy,set}.S

perf bench mem: Ignore export.h related changes to mem{cpy,set}.S

Ignore export.h and EXPORT_SYMBOL in:

  784d5699eddc ("x86: move exports to actual definitions")

We're not dragging this stuff, not useful in tools/

This silences the following warnings while building perf:

  Warning: tools/arch/x86/lib/memcpy_64.S differs from kernel
  Warning: tools/arch/x86/lib/memset_64.S differs from kernel

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/n/tip-h9vw3pe0fq79zmyqsfr0s0mo@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>