BUG: Support the fastcall mechanism for NumPy's ufunc methods
BUG: Support the fastcall mechanism for NumPy's ufunc methods

This is a start to support NumPy 1.21 use of FASTCALL methods
in ufuncs.  There are probably better ways to achieve this support.

NumPy further uses `tp_vectorcall_offset` on newer versions.  This
PR does not add support for this (meaning that a DUfunc will be
unnecessarily slow on NumPy >=1.21 when kwargs are used).

IntelLabs/numba,numba/numba,IntelLabs/numba,IntelLabs/numba,numba/numba,IntelLabs/numba,seibert/numba,numba/numba,cpcloud/numba,seibert/numba,seibert/numba,numba/numba,cpcloud/numba,IntelLabs/numba,cpcloud/numba,cpcloud/numba,numba/numba,seibert/numba,seibert/numba,cpcloud/numba