perf record: Add --dry-run option to check cmdline options

perf record: Add --dry-run option to check cmdline options

With '--dry-run', 'perf record' doesn't do reall recording. Combine with
llvm.dump-obj option, --dry-run can be used to help compile BPF objects
for embedded platform.

Signed-off-by: Wang Nan <wangnan0@huawei.com>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: pi3orama@163.com
Link: http://lkml.kernel.org/r/1466064161-48553-3-git-send-email-wangnan0@huawei.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>