- migrate to c++14 for most compilers *except* gcc.
There are still many systems in use with gcc-4.8.5, which does not
support c++14.
- initial rules for nvidia compilers (pgi is will soon be defunct).
Not fully tested...
CONFIG: provide fallback value for the user directory name
- in containers may have an unset USER env variable.
Default to 'user' to prevent ugly looking directory names.
