how to pass cuda arch settings to blt_cuda_smoke?

Nobody has claimed this yet.

Using blt fb5633c (master as of 6/13/19)

I have the following set in a host-config file:

```
set(CUDA_ARCH "sm_60" CACHE STRING "")
set(CMAKE_CUDA_ARCH "sm_60" CACHE STRING "")
set(CUDA_NVCC_FLAGS "-arch=sm_60" CACHE STRING "")
```
None of these propgate to the `blt_cuda_smoke` test, and I end up with an exe that is targeted at `sm_30`.

```
bash-4.2$ cuobjdump tests/blt_cuda_smoke

Fatbin elf code:
================
arch = sm_30
code version = [1,7]
producer = cuda
host = linux
compile_size = 64bit

Fatbin ptx code:
================
arch = sm_30
code version = [6,2]
producer = cuda
host = linux
compile_size = 64bit
compressed

Fatbin elf code:
================
arch = sm_30
code version = [1,7]
producer =
host = linux
compile_size = 64bit
```

Not sure how to pass flags?

Start by tracing how the host-config settings reach the blt_cuda_smoke target, focusing on CUDA_ARCH, CMAKE_CUDA_ARCH, and CUDA_NVCC_FLAGS. Use cuobjdump on the resulting executable to compare the configured architecture with the observed sm_30 output; done means the supported setting is identified and the target uses the requested architecture.

Written by the indexing model from the issue text.