Maybe simplify/speed up PIP installs

More convenient to override the whole platform name,
including architecture.

* probe:
  handle strings in MSVC object files
  add toolchain inspection

This small change fixes a problem when a common list object is used in setup.py to declare dependencies for multiple extension objects. In this case the library dependencies get accumulated in the same list which causes problems in more complex builds.

Since _dsoinfo.py is "standard" convention,
only allow specific override (or omission).

Generates an info module per DSO built with information on the original
dot separated name, the stem and full path to the DSO. The info module
also adds the directory containing the DSO to the DLL path on Windows
once the info module is loaded.

The name for the info module is configurable per DSO and defaults to
`"{stem}_dso.py"`. Setting the name to `None` turns off info moduel
generation for the DSO.

The change does not attempt to create proper package structure to ensure
the info modules are importable, that is up to the user.

needed on windows for py>=3.8

update classifiers in setup.py

When a package is installed in development mode by `pip install -e`, it
calls `python setup.py develop` under the covers

    https://setuptools.readthedocs.io/en/latest/setuptools.html#development-mode

However it currently skips build_dso in that mode which leads to build
failure if anything - e.g. extension - is depending on a dso:

    + pip install -v -e .
    Created temporary directory: /tmp/pip-ephem-wheel-cache-OJgoBO
    Created temporary directory: /tmp/pip-req-tracker-CrRj5z
    Created requirements tracker '/tmp/pip-req-tracker-CrRj5z'
    Created temporary directory: /tmp/pip-install-hiu8rq
    Obtaining file:///home/kirr/src/tools/py/pypa/setuptools_dso/example
      Added file:///home/kirr/src/tools/py/pypa/setuptools_dso/example to build tracker '/tmp/pip-req-tracker-CrRj5z'
      Running setup.py (path:/home/kirr/src/tools/py/pypa/setuptools_dso/example/setup.py) egg_info for package from file:///home/kirr/src/tools/py/pypa/setuptools_dso/example
        Running command python setup.py egg_info
        running egg_info
        creating src/dsodemo.egg-info
        writing src/dsodemo.egg-info/PKG-INFO
        writing top-level names to src/dsodemo.egg-info/top_level.txt
        writing dependency_links to src/dsodemo.egg-info/dependency_links.txt
        writing manifest file 'src/dsodemo.egg-info/SOURCES.txt'
        reading manifest file 'src/dsodemo.egg-info/SOURCES.txt'
        writing manifest file 'src/dsodemo.egg-info/SOURCES.txt'
      Source in /home/kirr/src/tools/py/pypa/setuptools_dso/example has version 0.1, which satisfies requirement dsodemo==0.1 from file:///home/kirr/src/tools/py/pypa/setuptools_dso/example
      Removed dsodemo==0.1 from file:///home/kirr/src/tools/py/pypa/setuptools_dso/example from build tracker '/tmp/pip-req-tracker-CrRj5z'
    Installing collected packages: dsodemo
      Running setup.py develop for dsodemo
        Running command /home/kirr/src/tools/py/pypa/setuptools_dso/env/bin/python -c "import setuptools, tokenize;__file__='/home/kirr/src/tools/py/pypa/setuptools_dso/example/setup.py';f=getattr(tokenize, 'open', open)(__file__);code=f.read().replace('\r\n', '\n');f.close();exec(compile(code, __file__, 'exec'))" develop --no-deps
        running develop
        Checking .pth file support in /home/kirr/src/tools/py/pypa/setuptools_dso/env/lib/python2.7/site-packages/
        /home/kirr/src/tools/py/pypa/setuptools_dso/env/bin/python -E -c pass
        TEST PASSED: /home/kirr/src/tools/py/pypa/setuptools_dso/env/lib/python2.7/site-packages/ appears to support .pth files
        running egg_info
        writing src/dsodemo.egg-info/PKG-INFO
        writing top-level names to src/dsodemo.egg-info/top_level.txt
        writing dependency_links to src/dsodemo.egg-info/dependency_links.txt
        reading manifest file 'src/dsodemo.egg-info/SOURCES.txt'
        writing manifest file 'src/dsodemo.egg-info/SOURCES.txt'
        running build_ext
        Traceback (most recent call last):
          File "<string>", line 1, in <module>
          File "/home/kirr/src/tools/py/pypa/setuptools_dso/example/setup.py", line 26, in <module>
            x_dsos = [dso],
          File "/home/kirr/src/tools/py/pypa/setuptools_dso/env/local/lib/python2.7/site-packages/setuptools_dso/__init__.py", line 37, in setup
            _setup(**kws)
          File "/home/kirr/src/tools/py/pypa/setuptools_dso/env/local/lib/python2.7/site-packages/setuptools/__init__.py", line 145, in setup
            return distutils.core.setup(**attrs)
          File "/usr/lib/python2.7/distutils/core.py", line 151, in setup
            dist.run_commands()
          File "/usr/lib/python2.7/distutils/dist.py", line 953, in run_commands
            self.run_command(cmd)
          File "/usr/lib/python2.7/distutils/dist.py", line 972, in run_command
            cmd_obj.run()
          File "/home/kirr/src/tools/py/pypa/setuptools_dso/env/local/lib/python2.7/site-packages/setuptools/command/develop.py", line 38, in run
            self.install_for_development()
          File "/home/kirr/src/tools/py/pypa/setuptools_dso/env/local/lib/python2.7/site-packages/setuptools/command/develop.py", line 140, in install_for_development
            self.run_command('build_ext')
          File "/usr/lib/python2.7/distutils/cmd.py", line 326, in run_command
            self.distribution.run_command(command)
          File "/usr/lib/python2.7/distutils/dist.py", line 972, in run_command
            cmd_obj.run()
          File "/home/kirr/src/tools/py/pypa/setuptools_dso/env/local/lib/python2.7/site-packages/setuptools_dso/dsocmd.py", line 395, in run
            _build_ext.run(self)
          File "/home/kirr/src/tools/py/pypa/setuptools_dso/env/local/lib/python2.7/site-packages/setuptools/command/build_ext.py", line 78, in run
            _build_ext.run(self)
          File "/usr/lib/python2.7/distutils/command/build_ext.py", line 340, in run
            self.build_extensions()
          File "/usr/lib/python2.7/distutils/command/build_ext.py", line 449, in build_extensions
            self.build_extension(ext)
          File "/home/kirr/src/tools/py/pypa/setuptools_dso/env/local/lib/python2.7/site-packages/setuptools_dso/dsocmd.py", line 406, in build_extension
            self.dso2lib_pre(ext)
          File "/home/kirr/src/tools/py/pypa/setuptools_dso/env/local/lib/python2.7/site-packages/setuptools_dso/dsocmd.py", line 146, in dso2lib_pre
            raise RuntimeError("Unable to find DSO %s needed by extension %s"%(dso, ext.name))
        RuntimeError: Unable to find DSO dsodemo.lib.demo needed by extension dsodemo.ext.dtest

-> Fix it by making build_ext to depend on build_dso.