Make the pyximport-pyimport tests more robust by testing that the file is compiled instead of looking at the "__file__" attribute.

This reverts commit e9435cd9.

Cython incorrectly generated (optimised) range code for "for i in range(1,2,3,4)" as if it saw "for i in range(1,2,3)".
This PR deactivates this optimization when too many arguments are provided, to match the behavior of Python.
Original patch by Max Bachmann.

Closes https://github.com/cython/cython/pull/4550

Closes https://github.com/cython/cython/issues/2770

Add missing import in doctest when the module is compiled (and StringIO has become a global cdef variable).

* Add a wrapper for posix <sys/uio.h>
* Add a script to generate tests for posix pxds
* Generate `tests/compile/posix_pxds.pyx`
* Update fcntl.pxd to POSIX.1-2017
* Update urls for posix/mman.pxd
* Update urls for posix/resource.pxd
* Add url for posix/select.pxd, and remove a `const`
* Update stat.pxd to POSIX.1-2017
* Update url for posix/wait.pxd

Closes https://github.com/cython/cython/issues/4522

Avoid pointing users to a link that just says "this section was moved to...". Just take them to the correct page first time.

This definition could be improved when variadic templates are supported at some point, but since the types are not really relevant for Cython it should be fine to use C variadics here (especially since I do not expect that variadic templates will be supported anytime soon).

Closes https://github.com/cython/cython/issues/2171

Closes https://github.com/cython/cython/issues/4313

Annotations attached to namenodes weren't correctly processed with "InterpretCompilerDirectivesTransform"

Closes https://github.com/cython/cython/issues/4514

Add a `visitchild()` helper method to VisitorTransform that correctly reassigns the result, which is easily forgotten.

For PyPy3.8 (the current release is 7.3.7)

* PyPy<7.3.8 declares a struct with the last fields tp_finalize, tp_print, tp_pypy_flags
* PyPy>=7.3.8 will declare a struct with the last fields tp_finalize, tp_vectorcall, tp_print

PyPy3.9 (not yet released) will declare a struct with the last fields tp_finalize, tp_vectorcall, tp_pypy_flags

See https://foss.heptapod.net/pypy/pypy/-/issues/3618

For PyPy3.8 (the current release is 7.3.7)

* PyPy<7.3.8 declares a struct with the last fields tp_finalize, tp_print, tp_pypy_flags
* PyPy>=7.3.8 will declare a struct with the last fields tp_finalize, tp_vectorcall, tp_print

PyPy3.9 (not yet released) will declare a struct with the last fields tp_finalize, tp_vectorcall, tp_pypy_flags

See https://foss.heptapod.net/pypy/pypy/-/issues/3618

Revert "Try to resolve build failures by switching back to CPython's distutils instead of using the one in setuptools 0.60."

This reverts commit 0ec33692.