Add "tp_pypy_flags" field to PyTypeObject struct when compiling in PyPy 6.0+ in order to avoid C compiler warnings about an uninitialised struct field.

This reverts commit f5aa00bb.

Closes https://github.com/cython/cython/issues/3938

Fixes an issue which Pyston triggers.
See https://github.com/cython/cython/issues/4200

Exception messages had changed a little

Let a tracing test run slower to prevent div-by-zero crashes in line_profiler due to measured zero runtime.

Python 3.11 hid _PyLong_FormatAdvancedWriter and
_PyFloat_FormatAdvancedWriter. I've disabled USE_UNICODE_WRITER
for the moment but I suspect we want to find replacements in the longer term.

To silence a compiler warning since it was added in Python 3.11a2.

For 0.29.x branch only.

With reference to https://github.com/cython/cython/issues/4365#issuecomment-977023011
in Python 3 PyCode_NewEmpty does everything we need to set
exception traceback code objects.

This change is probably only a real improvement on Py3.11 onwards
(where the replacement for PyCode_new is currently pretty slow).
On earlier version it'll probably be fairly similar (maybe one extra allocation for the cline case?)

* Initial support for Python 3.11 (GH-4414)

https://github.com/cython/cython/issues/4414

* Add a basic replacement for PyCode_New().

An optimized versions would be nice, but this is intended to work sufficiently to start testing. Also, CPython 3.11 might actually add a new C-API function to simplify setting the current code position. That might be used instead.

* Disable introspection of frame object with vectorcall

This feature looked to only be used for early Python versions that don't have the full vectorcall protocol (and the contents of the frame object are changed in Python 3.11).

* Use new C-API function to get the current frame on Python 3.11 alpha (GH-4427)

Use the accessor function instead of the direct struct member (which is now the wrong type).

https://github.com/cython/cython/issues/4427
Closes https://github.com/cython/cython/issues/4416

* Fix number of arguments

* Disable CYTHON_FAST_PYCALL for 3.11 in Cython 0.29.x due to non-trivial incompatibilities.

* Remove remanent of 3.8alpha/beta workaround for PyCode_New().

All the versions we currently test are new enough that the alias is no longer necessary.

The string comparison was reporting '11' < '4' (so OpenMP tests were being skipped on GCC 11)

Fixes https://github.com/cython/cython/issues/3647

Use newer test dependencies in Py3.6+. (Excluding 3.10 for now to give the projects a bit more time.)

Disable some plain Python (non Cython related) tests that fail in Py3.10 due to changed error messages.

Avoid "possible loss of data" warning in MSVC by adding redundant casts to code that gets discarded later.

Still requires the more conservative __index__ here rather than a possibly
truncating __int__ because this is used in a context where floating point
values should probably be treated specially.

This fixes Github issue #2752.