perf python: Remove -mcet and -fcf-protection when building with clang

These options are not present in older clang versions, so when we build
for a distro that has a gcc new enough to have these options and that
the distro python build config settings use them but clang doesn't
support, b00m.

This is the case with fedora 28 and rawhide, so check if clang has the
options and remove the missing ones from CFLAGS.

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: https://lkml.kernel.org/n/tip-7asds7yn6gzg6ns1lw17ukul@git.kernel.org


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>