Use process level locks for fork() only.
Use process level locks for fork() only.

As title.

Fixes #4348

IntelLabs/numba,numba/numba,stonebig/numba,numba/numba,stonebig/numba,IntelLabs/numba,stonebig/numba,gmarkall/numba,numba/numba,stuartarchibald/numba,cpcloud/numba,cpcloud/numba,cpcloud/numba,sklam/numba,sklam/numba,IntelLabs/numba,stonebig/numba,stuartarchibald/numba,seibert/numba,seibert/numba,sklam/numba,gmarkall/numba,seibert/numba,numba/numba,gmarkall/numba,seibert/numba,cpcloud/numba,IntelLabs/numba,sklam/numba,stuartarchibald/numba,numba/numba,stonebig/numba,seibert/numba,gmarkall/numba,gmarkall/numba,stuartarchibald/numba,stuartarchibald/numba,IntelLabs/numba,sklam/numba,cpcloud/numba