Added a new CUDA variable for specifying the CUDA_HOST_COMPILER.  This will allow users to
be able to specify which host compiler to use for invoking NVCC with.  By default it will
use the compiler used for host compilation.  This is convenient for when you want to
specify a different compiler than the default compiler.  You end up using the same
compiler for both the NVCC compilation and the host compilation instead of using the
default compiler in the path for NVCC.