Disable "unicode_imports" test in Py2 because it's too fiddly to get working on Windows/appveyor, also because Py2 distutils requires module names to be byte strings.

Fix cython.inline() in Py3.4 by making it use the legacy fallback code for extension module loading.

Remove add_dll_directory() calls in cython.inline() again to see if it's really needed after fixing the import procedure.

Try to make cython.inline() tests pass in Py3.8 on Windows by adhering to the recommended module loading pattern.

For srctree tests, include the test directory in the PYTHONPATH of subprocesses, but not in the own sys.path of the test runner.

Register the absolute module path in cython.inline() under Windows, not the (potentially) relative path.

* Rewrite the test code generation for the unicode normalisation test, making sure that we always write UTF-8 source files.

* Fix failures to print the compilation status for modules with non-ascii names (on Windows).

* Help with remote debugging environment encoding problems in test runs, by extending the output of the "buildenv" pseudo-test.

* Explicitly set I/O encoding for subprocesses in parallel cythonize() runs to make the test runner workers inherit it (instead of defaulting to ASCII in Py2).

* Use a Latin-1 Unicode character in the test for Unicode module names to make it more compatible with Windows file system character sets (such as CP-1252).

* Properly decode source and module file name from the FS encoding in Py2. Previously, with ASCII module names, UTF-8 decoding always worked, but wasn't correct.

* Hack around a distutils 3.[5678] bug on Windows for unicode module names.
https://bugs.python.org/issue39432

* Try to fix cython.inline() on Windows with Py3.8+ where the DLL loading requires an explicit registration of the extension output directory.
Closes GH-3450.

If your installation is faulty, cygdb will now print the filepath of the code that caused an exception, and the path of the python interpreter will be printed for better debugging.

See https://github.com/cython/cython/issues/3354

The directives are currently inherited from user code, which is not correct, but it seemed difficult to reliably change the directives applied to the `__pyx_fused_cpdef` dispatch function, so instead the code was changed to be independent.

Fixes https://github.com/cython/cython/issues/3492

Merge some runtime compilation runs into a single one in the CPython fstring test to reduce the overall runtime of the test.

Closes GH-3481.