scons,stdlib: Remove deprecated 'distutils' module

The Python module 'distutils' will be removed in Python 3.12:
https://docs.python.org/3/library/distutils.html

This patch removed usage of 'distutils' in the gem5 code base.

Change-Id: I1e3a944446149f3cd6cbf4211a1565b5f74c85a0
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/71679
Tested-by: kokoro <noreply+kokoro@google.com>
Maintainer: Jason Lowe-Power <power.jg@gmail.com>
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
(cherry picked from commit b182b15f93)
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/71741
Maintainer: Bobby Bruce <bbruce@ucdavis.edu>
Reviewed-by: Bobby Bruce <bbruce@ucdavis.edu>

src/SConscript

@@ -39,7 +39,7 @@
 
 import collections
 import copy
-import distutils.spawn
+from shutil import which
 import itertools
 import os
 import os.path
@@ -269,7 +269,7 @@ def ProtoBuf(source, tags=None, add_tags=None):
     '''Add a Protocol Buffer to build'''
     Source(source, tags, add_tags, append={'CXXFLAGS': '-Wno-array-bounds'})
 
-env['PROTOC_GRPC'] = distutils.spawn.find_executable('grpc_cpp_plugin')
+env['PROTOC_GRPC'] = which('grpc_cpp_plugin')
 if env['PROTOC_GRPC']:
     with Configure(env) as conf:
         if (not env['HAVE_PKG_CONFIG'] or