compilers: add arm compiler detection to Spack
compilers: add arm compiler detection to Spack

- added arm.py with support for detecting `armclang` and `armflang`

Co-authored-by: Srinath Vadlamani <0dbb97c794b0b111f6f3e104db6d37ddeceb62cb@arm.com>

LLNL/spack,iulian787/spack,LLNL/spack,LLNL/spack,iulian787/spack,iulian787/spack,LLNL/spack,iulian787/spack,iulian787/spack,LLNL/spack