Example replacement:
```
'-D(\w+)(:BOOL)?=\{0\}'\.\s*format\s*\(\s*'(ON|YES|true|TRUE)' if '\+(\w+)' in (self\.)?spec else '(OFF|NO|false|FALSE)'\)
```
with
```
self.define_from_variant('\1', '\4')
```
This will cause failures if any variants were misspelled: I have already caught two packages with nonexistent variants.
- [x] add `concretize.lp`, `spack.yaml`, etc. to licensed files
- [x] update all licensed files to say 2013-2021 using
`spack license update-copyright-year`
- [x] appease mypy with some additions to package.py that needed
for oneapi.py
- 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
