initial commit of CUDA test integrator
Reorganize the way flags are passed to src files

Since nvcc apparently only works with gcc, need to exclude
any flags which may cause gcc to crash. These include everything
returned by llvm-config if compiling with Clang. New layout:
only pass LLVM_FLAGS to the LLVM component (and the GPU component,
where required)
add proxy to safely create GPU int
fix docs/comments
link in temp GPU code
test launching CUDA device func - it works