Add debug guard to debug only C function.
Add debug guard to debug only C function.

As title. Stops the compilers rightly complaining about this
function being unused when compiling at release levels.

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