[Bug other/101166] Add SPDX license identifiers

[egallager at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101166

--- Comment #3 from Eric Gallager <egallager at gcc dot gnu.org> ---
The FSFE's REUSE tool could be helpful for this: 
https://github.com/fsfe/reuse-tool