- 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
* AutotoolsPackage: added configure_directory to permit build out of source. The configure script executable is now invoked with an absolute path. Modified a few packages accordingly.
* build_systems: functions returning directories are now properties
* build_systems: fixed issues with tcl and tk
* AutotoolsPackage: reworked recipe for autoreconf