* Add nvhpc compiler definition: "spack compiler add" will now look
for instances of the NVIDIA HPC SDK compiler executables
(nvc, nvc++, nvfortran) in supplied paths
* Add the nvhpc package which installs the nvhpc compiler
* Add testing for nvhpc detection and C++-standard/pic flags
Co-authored-by: Scott McMillan <smcmillan@nvidia.com>
