[libcxx] Replace func_name with __name__ for compatibility with Python 3

[broadwaylamb]

Summary

The __name__ attribute is the correct way to get a function name in
Python 3. This also works with Python 2.

[broadwaylamb]

Replace one more func_name

[jroelofs]

LGTM

libcxx/utils/libcxx/test/tracing.py

 #===----------------------------------------------------------------------===##
 #
 # Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 # See https://llvm.org/LICENSE.txt for license information.
 # SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 #
 #===----------------------------------------------------------------------===##
 
 import os
 import inspect
 
 
 def trace_function(function, log_calls, log_results, label=''):
     def wrapper(*args, **kwargs):
         kwarg_strs = ['{}={}'.format(k, v) for (k, v) in kwargs]
         arg_str = ', '.join([str(a) for a in args] + kwarg_strs)
-        call_str = '{}({})'.format(function.func_name, arg_str)
+        call_str = '{}({})'.format(function.__name__, arg_str)
 
         # Perform the call itself, logging before, after, and anything thrown.
         try:
             if log_calls:
                 print('{}: Calling {}'.format(label, call_str))
             res = function(*args, **kwargs)
             if log_results:
                 print('{}: {} -> {}'.format(label, call_str, res))