Build system: use SPDX identifiers The SPDX identifiers [1] are a legally binding shorthand, which can be used instead of the full boiler plate text. This is the first step towards implementing the full REUSE spec [2] to help with copyright and licensing audits and compliance. This will reduce a lot a manual work required for the licensing audit required in Debian on each update. For files that lacked copyright and licensing information, I used the following guidelines. If a clear author could be determined from the git history use it, otherwise use 'EfficiOS Inc.'. For build system files, use 'MIT', for documentation 'CC-BY-4.0' and for data files 'CC-1.0'. [1] https://spdx.org/ids-how [2] https://reuse.software/tutorial/ Change-Id: Ie507130c00b95606dc439616fda4fd9b1d35353d Signed-off-by: Michael Jeanson <mjeanson@efficios.com> Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>