perf tools: Add missing object file to the python binding linkage list

In ac12f6764c ("perf tools: Implement branch_type event parameter") we
started using the parse_branch_str() function from one of the files used
in the python binding, which caused this entry in 'perf test' to fail:

  # perf test -v python
  16: Try 'import perf' in python, checking link problems      :
  --- start ---
  test child forked, pid 16667
  Traceback (most recent call last):
    File "<stdin>", line 1, in <module>
  ImportError: /tmp/build/perf/python/perf.so: undefined symbol:
  parse_branch_str
  test child finished with -1
  ---- end ----
  Try 'import perf' in python, checking link problems: FAILED!
  #

I must've commited some mistake when running 'perf test' to send the
pull request for the perf-core-for-mingo-20161024 tag, to have let this
regression to pass, sigh.

Just add tools/perf/util/parse-branch-options.c and switch from using
ui__warning(), that is not available in the python binding, use
pr_warning() instead, which is good enough for this case.

Now:

  # perf test python
  16: Try 'import perf' in python, checking link problems      : Ok
  #

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>
Cc: Andi Kleen <ak@linux.intel.com>
Fixes: ac12f6764c ("perf tools: Implement branch_type event parameter")
Link: http://lkml.kernel.org/n/tip-9kn1ct1cx9ppwqlmzl6z0xhs@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/parse-branch-options.c

@@ -64,7 +64,7 @@ int parse_branch_str(const char *str, __u64 *mode)
 		}
 		if (!br->name) {
 			ret = -1;
-			ui__warning("unknown branch filter %s,"
+			pr_warning("unknown branch filter %s,"
 				    " check man page\n", s);
 			goto error;
 		}

tools/perf/util/python-ext-sources

@@ -18,6 +18,7 @@ util/thread_map.c
 util/util.c
 util/xyarray.c
 util/cgroup.c
+util/parse-branch-options.c
 util/rblist.c
 util/counts.c
 util/strlist.c