BLD: Compatibility issues with master branch cython
Continuation of issue #33224

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With the latest version of cython, running ```python setup.py build_ext --inplace -j 0``` gives the following errors:

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#### ```pandas/_libs/join.pyx```:

<details>

```
building 'pandas._libs.join' extension
gcc -pthread -Wno-unused-result -Wsign-compare -DNDEBUG -g -fwrapv -O3 -Wall -march=x86-64 -mtune=generic -O3 -pipe -fno-plt -fno-semantic-interposition -march=x86-64 -mtune=generic -O3 -pipe -fno-plt -march=x86-64 -mtune=generic -O3 -pipe -fno-plt -fPIC -DNPY_NO_DEPRECATED_API=0 -Ipandas/_libs/src/klib -I/home/user/Venvs/cythonM-pandas/lib/python3.8/site-packages/numpy/core/include -I/home/user/Venvs/cythonM-pandas/include -I/usr/include/python3.8 -c pandas/_libs/join.c -o build/temp.linux-x86_64-3.8/pandas/_libs/join.o
In file included from /usr/include/python3.8/tupleobject.h:41,
                 from /usr/include/python3.8/Python.h:105,
                 from pandas/_libs/join.c:32:
pandas/_libs/join.c: In function ‘__pyx_pf_6pandas_5_libs_4join_12inner_join_indexer.isra.0’:
/usr/include/python3.8/cpython/tupleobject.h:27:60: warning: array subscript -1 is below array bounds of ‘PyObject *[1]’ {aka ‘struct _object *[1]’} [-Warray-bounds]
   27 | #define PyTuple_GET_ITEM(op, i) (_PyTuple_CAST(op)->ob_item[i])
      |                                 ~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~
pandas/_libs/join.c:204503:27: note: in expansion of macro ‘PyTuple_GET_ITEM’
204503 |             PyObject *r = PyTuple_GET_ITEM(o, n);
       |                           ^~~~~~~~~~~~~~~~
pandas/_libs/join.c: In function ‘__pyx_pf_6pandas_5_libs_4join_10left_join_indexer.isra.0’:
/usr/include/python3.8/cpython/tupleobject.h:27:60: warning: array subscript -1 is below array bounds of ‘PyObject *[1]’ {aka ‘struct _object *[1]’} [-Warray-bounds]
   27 | #define PyTuple_GET_ITEM(op, i) (_PyTuple_CAST(op)->ob_item[i])
      |                                 ~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~
pandas/_libs/join.c:204503:27: note: in expansion of macro ‘PyTuple_GET_ITEM’
204503 |             PyObject *r = PyTuple_GET_ITEM(o, n);
       |                           ^~~~~~~~~~~~~~~~
pandas/_libs/join.c: In function ‘__pyx_pf_6pandas_5_libs_4join_8left_join_indexer_unique.isra.0’:
/usr/include/python3.8/cpython/tupleobject.h:27:60: warning: array subscript -1 is below array bounds of ‘PyObject *[1]’ {aka ‘struct _object *[1]’} [-Warray-bounds]
   27 | #define PyTuple_GET_ITEM(op, i) (_PyTuple_CAST(op)->ob_item[i])
      |                                 ~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~
pandas/_libs/join.c:204503:27: note: in expansion of macro ‘PyTuple_GET_ITEM’
204503 |             PyObject *r = PyTuple_GET_ITEM(o, n);
       |                           ^~~~~~~~~~~~~~~~
pandas/_libs/join.c: In function ‘__pyx_pf_6pandas_5_libs_4join_14outer_join_indexer.isra.0’:
/usr/include/python3.8/cpython/tupleobject.h:27:60: warning: array subscript -1 is below array bounds of ‘PyObject *[1]’ {aka ‘struct _object *[1]’} [-Warray-bounds]
   27 | #define PyTuple_GET_ITEM(op, i) (_PyTuple_CAST(op)->ob_item[i])
      |                                 ~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~
pandas/_libs/join.c:204503:27: note: in expansion of macro ‘PyTuple_GET_ITEM’
204503 |             PyObject *r = PyTuple_GET_ITEM(o, n);
       |                           ^~~~~~~~~~~~~~~~
```

</details>

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#### ```pandas/_libs/reshape.pyx```:

<details>

```
building 'pandas._libs.reshape' extension
gcc -pthread -Wno-unused-result -Wsign-compare -DNDEBUG -g -fwrapv -O3 -Wall -march=x86-64 -mtune=generic -O3 
-pipe -fno-plt -fno-semantic-interposition -march=x86-64 -mtune=generic -O3 -pipe -fno-plt -march=x86-64 -mtun
e=generic -O3 -pipe -fno-plt -fPIC -DNPY_NO_DEPRECATED_API=0 -I/home/user/Venvs/cythonM-pandas/lib/python3.8/
site-packages/numpy/core/include -I/home/user/Venvs/cythonM-pandas/include -I/usr/include/python3.8 -c pandas
/_libs/reshape.c -o build/temp.linux-x86_64-3.8/pandas/_libs/reshape.o
In file included from /usr/include/python3.8/tupleobject.h:41,
                 from /usr/include/python3.8/Python.h:105,
                 from pandas/_libs/reshape.c:30:
pandas/_libs/reshape.c: In function ‘__pyx_pf_6pandas_5_libs_7reshape_unstack.isra.0’:
/usr/include/python3.8/cpython/tupleobject.h:27:60: warning: array subscript -1 is below array bounds of ‘PyObject *[1]’ {aka ‘struct _object *[1]’} [-Warray-bounds]
   27 | #define PyTuple_GET_ITEM(op, i) (_PyTuple_CAST(op)->ob_item[i])
      |                                 ~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~
pandas/_libs/reshape.c:29728:27: note: in expansion of macro ‘PyTuple_GET_ITEM’
29728 |             PyObject *r = PyTuple_GET_ITEM(o, n);
      |                           ^~~~~~~~~~~~~~~~
```
</details>

---

[join_zip.zip](https://github.com/pandas-dev/pandas/files/4445598/join_zip.zip)

[reshape_zip.zip](https://github.com/pandas-dev/pandas/files/4445599/reshape_zip.zip)

---

Output of ```pd.show_versions()```:

<details>


INSTALLED VERSIONS
------------------
commit           :  bd91f4577c5b54a72a4e092a7d7db43fec1b46bb
python           : 3.8.2.final.0
python-bits      : 64
OS               : Linux
OS-release       : 5.5.13.b-1-hardened
machine          : x86_64
processor        : 
byteorder        : little
LC_ALL           : None
LANG             : en_US.UTF-8
LOCALE           : en_US.UTF-8

pandas           : 1.1.0.dev0+1159.gbd91f4577
numpy            : 1.18.2
pytz             : 2019.3
dateutil         : 2.8.1
pip              : 20.0.2
setuptools       : 46.1.3
Cython           : 3.0a0 (https://github.com/cython/cython/tree/30c891e0dc36a553455df9064ecb1f13414a12d2)
pytest           : None
hypothesis       : None
sphinx           : None
blosc            : None
feather          : None
xlsxwriter       : None
lxml.etree       : None
html5lib         : None
pymysql          : None
psycopg2         : None
jinja2           : None
IPython          : 7.13.0
pandas_datareader: None
bs4              : None
bottleneck       : None
fastparquet      : None
gcsfs            : None
lxml.etree       : None
matplotlib       : None
numexpr          : None
odfpy            : None
openpyxl         : None
pandas_gbq       : None
pyarrow          : None
pytables         : None
pytest           : None
pyxlsb           : None
s3fs             : None
scipy            : None
sqlalchemy       : None
tables           : None
tabulate         : None
xarray           : None
xlrd             : None
xlwt             : None
xlsxwriter       : None
numba            : None

</details>


