[clang] Replace find_executable with shutil.which in creduce script

[DavidSpickett]

Summary

distutils is deprecated and shutil.which is the suggested
replacement for this function.

https://peps.python.org/pep-0632/#migration-advice
https://docs.python.org/3/library/shutil.html#shutil.which

which was added in 3.3 (https://docs.python.org/3/library/shutil.html#shutil.which)
and LLVM requires at least 3.6 (https://llvm.org/docs/GettingStarted.html#software).

There is one small differnce here that shutil.which ignores the PATH
when given a path argument. However in this case I think that's actually
the behaviour we want.

[zequanwu]

LGTM.

clang/utils/creduce-clang-crash.py

 #!/usr/bin/env python3
 """Calls C-Reduce to create a minimal reproducer for clang crashes.
 
 Output files:
   *.reduced.sh -- crash reproducer with minimal arguments
   *.reduced.cpp -- the reduced file
   *.test.sh -- interestingness test for C-Reduce
 """
 
 from __future__ import print_function
 from argparse import ArgumentParser, RawTextHelpFormatter
 import os
 import re
+import shutil
 import stat
 import sys
 import subprocess
 import pipes
 import shlex
 import tempfile
 import shutil
-from distutils.spawn import find_executable
 import multiprocessing
 
 verbose = False
 creduce_cmd = None
 clang_cmd = None
 
 def verbose_print(*args, **kwargs):
   if verbose:
     print(*args, **kwargs)
 
 def check_file(fname):
   fname = os.path.normpath(fname)
   if not os.path.isfile(fname):
     sys.exit("ERROR: %s does not exist" % (fname))
   return fname
 
 def check_cmd(cmd_name, cmd_dir, cmd_path=None):
   """
   Returns absolute path to cmd_path if it is given,
   or absolute path to cmd_dir/cmd_name.
   """
   if cmd_path:
     # Make the path absolute so the creduce test can be run from any directory.
     cmd_path = os.path.abspath(cmd_path)
-    cmd = find_executable(cmd_path)
+    cmd = shutil.which(cmd_path)
     if cmd:
       return cmd
     sys.exit("ERROR: executable `%s` not found" % (cmd_path))
 
-  cmd = find_executable(cmd_name, path=cmd_dir)
+  cmd = shutil.which(cmd_name, path=cmd_dir)
   if cmd:
     return cmd
 
   if not cmd_dir:
     cmd_dir = "$PATH"
   sys.exit("ERROR: `%s` not found in %s" % (cmd_name, cmd_dir))
 
 def quote_cmd(cmd):