Update setup of LNT to handle python 3.12+ (#414)

Virtualenv in python 3.12+ no longer installs setuptools by default, see
[1]. This patch adds a "pip install setuptools" step to ClangBuilder.py,
which seems to be the only place we use virtualenv.

Note that running
$ VIRTUALENV_SETUPTOOLS=bundle virtualenv sandbox
as suggested in virtualenv release notes [2] will install an
older/incompatible version of setuptools, at least on Ubuntu 24.04
system.

[1] https://virtualenv.pypa.io/en/latest/user_guide.html#seeders
[2] https://virtualenv.pypa.io/en/latest/changelog.html#features-20-23-0

Author: maxim-kuvyrkov

zorg/buildbot/builders/ClangBuilder.py

@@ -615,6 +615,12 @@ def _getClangCMakeBuildFactory(
                                description='recreating sandbox',
                                workdir='test',
                                env=env))
+        f.addStep(ShellCommand(name='install lnt dependencies',
+                               command=[python, '-m', 'pip', 'install', 'setuptools'],
+                               haltOnFailure=True,
+                               description='install lnt dependencies',
+                               workdir='test/sandbox',
+                               env=env))
         f.addStep(ShellCommand(name='setup lit',
                                command=[python, lnt_setup, 'develop'],
                                haltOnFailure=True,