setup: handle removal of old MSVC compiler from setuptools 65.0 (issue6910)

It was removed a few years ago[1].  When trying to reproduce locally using a
clean py3.12 as called out in the bug report, `setuptools` wasn't installed at
all, and needed a `pip install` to fix a `ModuleNotFoundError` when building
locally.  Maybe that needs to be in the requirements clause now.

It looks like this "private" module was added in setuptools 48.0.[2]  I can't
find a changelog of what version was included in which version of python, and
the changelog for pip has a huge gap between when it called out 67.6.1 in `pip`
23.1 (2023-04-15), and 41.4.0 in `pip` 19.3 (2019-10-14).[3]  So, we'll just add
to the existing code instead of replacing it, for safety.

[1] https://github.com/pypa/setuptools/commit/cc017c77948737d131f683e0c25cd37bc639b8fc
[2] https://github.com/pypa/setuptools/commit/d034a5ec7f707499139f90eb846b9e720923124c
[3] https://pip.pypa.io/en/stable/news/

setup.py

@@ -1662,7 +1662,11 b" if os.name == 'nt':"
     # Allow compiler/linker flags to be added to Visual Studio builds.  Passing
     # extra_link_args to distutils.extensions.Extension() doesn't have any
     # effect.
+    try:
+        # setuptools < 65.0
     from distutils import msvccompiler
+    except ImportError:
+        from distutils import _msvccompiler as msvccompiler
 
     msvccompilerclass = msvccompiler.MSVCCompiler