According to the docs, "/Od" is the default in MSVC, so in order to get it, it should be enough to clear CFLAGS.
Setting it generates warnings in Py3.9 on appveyor ("source file '"/Od"' ignored"), suggesting that the option is not recognised as such.
https://docs.microsoft.com/en-us/cpp/build/reference/od-disable-debug?view=msvc-160

Remove "PYTHONHOME" setting from embed-test since it seems to break the I/O encoding setup in (at least) Py3.8+ venvs.

Signed-off-by: Andrew V. Jones <andrew.jones@vector.com>

Closes https://github.com/cython/cython/pull/4101
See https://github.com/cython/cython/issues/4100

* Handle constant folding for LanguageLevel 2 on Python 3. Ensure that when StrNode is a BytesLiteral, that we don't coerce it to unicode.
* Add test for string multiplication bug. Needed to change the TreePath slightly to allow bytes-to-str comparison.

Fixes https://github.com/cython/cython/issues/3951

Remove incorrect dict unpacking optimisation that leaked external dict changes into the result (GH-4091)

Closes https://github.com/cython/cython/issues/3227

* Disable GC-sensitive NumPy tests on PyPy
* Removed @testcase decorator pattern that was causing tests to be run twice

Creating global CDEFS for holding compiler definitions. Then pass it to the distutils.

Also add .vscode folder to .gitignore

Fixes https://github.com/cython/cython/issues/4096

Remove incorrect dict unpacking optimisation that leaked external dict changes into the result (GH-4091)

Closes https://github.com/cython/cython/issues/3227

Closes https://github.com/cython/cython/issues/4113

Replace usage of the seemingly CPython-internal Py_ISSPACE() macro by a dedicated inline function to make it work in C++ (where Py_ISSPACE() fails to link).

Closes https://github.com/cython/cython/issues/4111
Closes https://github.com/cython/cython/pull/4112

* Handle constant folding for LanguageLevel 2 on Python 3. Ensure that when StrNode is a BytesLiteral, that we don't coerce it to unicode.
* Add test for string multiplication bug. Needed to change the TreePath slightly to allow bytes-to-str comparison.

Fixes https://github.com/cython/cython/issues/3951

Fix optimised_pow2_inplace() doctest on Python 3.10 because the error message changed.

Python 3.9 error message:
    unsupported operand type(s) for ** or pow(): 'int' and 'str'

Python 3.10 error message:
    unsupported operand type(s) for **=: 'int' and 'str'

Re-disable third-party integration testing in Py2.6 entirely since most packages aren't compatible anymore (and I don't want to dig up the versions that are).