New compiler: nvhpc (NVIDIA HPC SDK) (#19294)

* 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>

lib/spack/env/cc

@@ -107,19 +107,19 @@ case "$command" in
     cpp)
         mode=cpp
         ;;
-    cc|c89|c99|gcc|clang|armclang|icc|pgcc|xlc|xlc_r|fcc)
+    cc|c89|c99|gcc|clang|armclang|icc|pgcc|nvc|xlc|xlc_r|fcc)
         command="$SPACK_CC"
         language="C"
         comp="CC"
         lang_flags=C
         ;;
-    c++|CC|g++|clang++|armclang++|icpc|pgc++|xlc++|xlc++_r|FCC)
+    c++|CC|g++|clang++|armclang++|icpc|pgc++|nvc++|xlc++|xlc++_r|FCC)
         command="$SPACK_CXX"
         language="C++"
         comp="CXX"
         lang_flags=CXX
         ;;
-    ftn|f90|fc|f95|gfortran|flang|armflang|ifort|pgfortran|xlf90|xlf90_r|nagfor|frt)
+    ftn|f90|fc|f95|gfortran|flang|armflang|ifort|pgfortran|nvfortran|xlf90|xlf90_r|nagfor|frt)
         command="$SPACK_FC"
         language="Fortran 90"
         comp="FC"

lib/spack/env/nvhpc/nvc

@@ -0,0 +1 @@
+../cc

lib/spack/env/nvhpc/nvc++

@@ -0,0 +1 @@
+../cc

lib/spack/env/nvhpc/nvfortran

@@ -0,0 +1 @@
+../cc