- 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
Several packages specified pkg-config as a dependency, which is
a specific implementation of the pkgconfig virtual. Most packages
do not request a specific implementation. The current concretizer
may choose a different implentation of pkgconfig for the nonspecific
dependents, which conflicts with the request for pkg-config. This
replaces all requests for a specific implementation of pkgconfig
with the virtual package as a temporary solution to the issue.
