Fix #5836: Passing opt=0 to NVVM doesn't work
Fix #5836: Passing opt=0 to NVVM doesn't work

With this change, `-opt=0` is now correctly passed to NVVM when `opt=0`
is in the `options` dict passed to `CompilationUnit.compile()`.

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