5fd9df0ed0
Add license information to files. Mostly automated with:
find src/ -name '*.[c,h]' | xargs sed -i '1s,^,// SPDX-License-Identifier: GPL-3.0-only\n\n,'
find src/ -name '*.mk' | xargs sed -i '1s,^,# SPDX-License-Identifier: GPL-3.0-only\n\n,'