llvm: various updates (#10427)
llvm: various updates (#10427)

* llvm: Bump version to 7.0.1

* llvm: Added perl-data-dumper build dependency for openmp

* llvm: Enable exception handling and RTTI

Useful to have turned on in general with RTTI but also necessary
to workaround some lldb stability issues with some versions of
libstdc++.

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