CUDA: Fix default selection of host compiler used to drive linking
When no explicit CMAKE_CUDA_HOST_COMPILER is specified by the user
then we do not pass -ccbin to nvcc. In this case, nvcc's link line
we extract during the compiler identification step may not have the
absolute path to the host compiler it uses to drive linking. If it is
not absolute, use the PATH= from nvcc's output to search for it since
that is the one nvcc would use.
This fixes our internal CMAKE_CUDA_HOST_LINK_LAUNCHER value used to
construct link lines when using CUDA as the linker language. It needs
to match the host compiler nvcc uses internally during compilation.
Fixes: #17323 (closed)