- remove the old LGPL license headers from all files in Spack
- add SPDX headers to all files
- core and most packages are (Apache-2.0 OR MIT)
- a very small number of remaining packages are LGPL-2.1-only
Flang now uses its own version of llvm and clang (called flang-driver). This is
handled by adding flang-specific versions of the LLVM package and updates flang
to depend on those versions.
