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.

In the next patch we will need to inject build_ext -> build_dso
dependency and will use this infrastructure.

- they are not used in the example
- they are injected as command classes by setuptools_dso.setup itself

Only need to include @loader_path/. if a dependency
is in the same directory.

@loader_path prefix requires dependent libraries to be in the same
directory or to use install_name_tool to change the name after linking.
With this fix, linker's -rpath can be used instead.

Which requires freeze_support()

Try to avoid problems only detectable in tag builds.

Expedite recommendation by Cython authors to distribute
generated c/c++ source files.

package_dir needs to be taken into account for inplace builds, because
then inplace directory of a package != directory of the package when it
is installed. For example setuptools_dso itself uses
`package_dir={'':'src'}` in its setup.py and this way for inplace build the
directory of setuptools_dso package is not setuptools_dso/ but
src/setuptools_dso/ instead.

However `build_dso --inplace` was installing built libraries without
taking package_dir into account. For example with amended example/ test,
libdemo.so was installed into dsodemo/lib/libdemo.so instead of
src/dsodemo/lib/libdemo.so, while dtest.so was correctly installed into
src/dsodemo/ext/dtest.so . As the result it was not working:

    + python -m dsodemo.cli
    Traceback (most recent call last):
      File "/usr/lib/python2.7/runpy.py", line 174, in _run_module_as_main
        "__main__", fname, loader, pkg_name)
      File "/usr/lib/python2.7/runpy.py", line 72, in _run_code
        exec code in run_globals
      File "/home/kirr/src/tools/py/pypa/setuptools_dso/example/src/dsodemo/cli.py", line 15, in <module>
        from .ext import dtest
    ImportError: libdemo.so.1.0: cannot open shared object file: No such file or directory
    .../setuptools_dso$ ll example/
    итого 16
    drwxr-xr-x 4 kirr kirr 4096 дек  4 18:12 build
    drwxr-xr-x 3 kirr kirr 4096 дек  4 18:12 dsodemo
    -rwxr-xr-x 1 kirr kirr  639 дек  4 18:12 setup.py
    drwxr-xr-x 3 kirr kirr 4096 дек  4 18:06 src
    .../setuptools_dso$ ll example/dsodemo/lib/
    итого 136
    -rwxr-xr-x 1 kirr kirr 68888 дек  4 18:12 libdemo.so
    -rwxr-xr-x 1 kirr kirr 68888 дек  4 18:12 libdemo.so.1.0
    .../setuptools_dso$ ll example/src/dsodemo/ext/
    итого 124
    -rwxr-xr-x 1 kirr kirr 119000 дек  4 18:12 dtest.so
    -rw-r--r-- 1 kirr kirr      0 июл 30 21:37 __init__.py
    -rw-r--r-- 1 kirr kirr    110 дек  4 18:12 __init__.pyc
    .../setuptools_dso$ ldd example/src/dsodemo/ext/dtest.so
            linux-vdso.so.1 (0x00007fffae3fd000)
            libdemo.so.1.0 => not found
            libstdc++.so.6 => /usr/lib/x86_64-linux-gnu/libstdc++.so.6 (0x00007f1c3bf20000)
            libm.so.6 => /lib/x86_64-linux-gnu/libm.so.6 (0x00007f1c3bd9d000)
            libgcc_s.so.1 => /lib/x86_64-linux-gnu/libgcc_s.so.1 (0x00007f1c3bd83000)
            libpthread.so.0 => /lib/x86_64-linux-gnu/libpthread.so.0 (0x00007f1c3bd62000)
            libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007f1c3bba1000)
            /lib64/ld-linux-x86-64.so.2 (0x00007f1c3c149000)
    .../setuptools_dso$ objdump -x example/src/dsodemo/ext/dtest.so |grep PATH
      RUNPATH              \$ORIGIN/../lib:$ORIGIN/../lib

-> Fix it by taking package_dir option into account in --inplace dsocmd handler.

Note1: The code to do so mimics build_ext from setuptools:

    https://github.com/pypa/setuptools/blob/v42.0.2-0-g1d03fdc9/setuptools/command/build_ext.py#L89-L107

Note2: Sources of Extension and DSO are specified with full path from project
top-level, because it already works this way for unmodified Extension even in
presence of package_dir.

Don't allow one to pass into setuptools_dso.setup() e.g. build_ext that
does not inherit from setuptools_dso.build_ext.

Fixes: 67d717a6 (wrapper setup don't clobber)