Comment 3 for bug 1937261

From buildlog of msgpack on bionic/ussuri:

cythonize: 'msgpack/_cmsgpack.pyx'

Error compiling Cython file:
------------------------------------------------------------
...
# coding: utf-8

from cpython cimport *
from cpython.bytearray cimport PyByteArray_Check, PyByteArray_CheckExact
^
------------------------------------------------------------

msgpack/_packer.pyx:4:0: 'cpython/bytearray.pxd' not found

Error compiling Cython file:
------------------------------------------------------------
...
# coding: utf-8

from cpython cimport *
from cpython.bytearray cimport PyByteArray_Check, PyByteArray_CheckExact
^
------------------------------------------------------------

msgpack/_packer.pyx:4:0: 'cpython/bytearray/PyByteArray_Check.pxd' not found

Error compiling Cython file:
------------------------------------------------------------
...
# coding: utf-8

from cpython cimport *
from cpython.bytearray cimport PyByteArray_Check, PyByteArray_CheckExact
^
------------------------------------------------------------

msgpack/_packer.pyx:4:0: 'cpython/bytearray/PyByteArray_CheckExact.pxd' not found

Error compiling Cython file:
------------------------------------------------------------
...
cdef int DEFAULT_RECURSE_LIMIT=511
cdef long long ITEM_LIMIT = (2**32)-1

cdef inline int PyBytesLike_Check(object o):
    return PyBytes_Check(o) or PyByteArray_Check(o)
                                               ^
------------------------------------------------------------

msgpack/_packer.pyx:49:48: 'PyByteArray_Check' is not a constant, variable or function identifier

Error compiling Cython file:
------------------------------------------------------------
...
cdef inline int PyBytesLike_Check(object o):
    return PyBytes_Check(o) or PyByteArray_Check(o)

cdef inline int PyBytesLike_CheckExact(object o):
    return PyBytes_CheckExact(o) or PyByteArray_CheckExact(o)
                                                         ^
------------------------------------------------------------

msgpack/_packer.pyx:53:58: 'PyByteArray_CheckExact' is not a constant, variable or function identifier