The -spec=/path/to/file can be used to change what gcc puts in the cc,
ld, etc command lines, but this is not present in clang, filter it out
at the setup.py file by changing python2's internal variable where it
keeps its initial CFLAGS value.

With this all of perf can be built in at least Fedora 25, fixing this
problem:

    GEN      /tmp/build/perf/python/perf.so
    CC       /tmp/build/perf/builtin-buildid-list.o
  clang-4.0: error: argument unused during compilation: '-specs=/usr/lib/rpm/redhat/redhat-hardened-cc1' [-Werror,-Wunused-command-line-argument]
  clang-4.0: error: argument unused during compilation: '-specs=/usr/lib/rpm/redhat/redhat-hardened-cc1' [-Werror,-Wunused-command-line-argument]
  error: command 'clang' failed with exit status 1

Now I need to change all the containers where I have clang to build
perf with it, so that we can check that in other distros (opensuse, debian,
ubuntu, etc) this also works.

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-g9lhgr162ao8ao29vvf0hgm1@git.kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>