tools perf scripting python: clang doesn't have -spec, remove it

tools perf scripting python: clang doesn't have -spec, remove it

Gcc has a -spec option to override what options to pass to cc, etc, and
in some distros this is used, like in fedora, where we end up getting
this passed to gcc that makes clang, that doesn't have this option to
stop the build:

  CC       /tmp/build/perf/util/scripting-engines/trace-event-python.o
clang-4.0: error: argument unused during compilation: '-specs=/usr/lib/rpm/redhat/redhat-hardened-cc1' [-Werror,-Wunused-command-line-argument]

So filter this out when the compiler used is clang, this way we
can build the python scripting support in tools/perf/.

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-2gosxoiouf24pnlknp7w7q4z@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>