Update licensing info for 1.18 snap package

[WebDrake]

This PR fixes the description of the LLVM license (Apache 2.0 for LLVM 9+, which is what this version of the package uses) and updates copyright years for LDC and DMD/druntime/phobos.

SPDX licensing metadata has also been added to the snap package config.

Some of these changes should probably be pushed upstream to the main LDC project, but they need to be made in the snap package anyway.

[WebDrake]

Whoops, it turns out that snapcraft/snapd require SPDX 2.x identifiers. Fixed, and noted this in the commit message.

diff --git a/snap/snapcraft.yaml b/snap/snapcraft.yaml
index c838713..0171f08 100644
--- a/snap/snapcraft.yaml
+++ b/snap/snapcraft.yaml
@@ -10,7 +10,7 @@ description: |
 base: core
 confinement: classic
 grade: stable
-license: BSD-3-Clause AND BSL-1.0 AND Zlib AND Apache-2.0 AND NCSA AND (Artistic-1.0 OR GPL-2.0-or-later)
+license: BSD-3-Clause AND BSL-1.0 AND Zlib AND Apache-2.0 AND NCSA AND (Artistic-1.0 OR GPL-2.0+)

 apps:
   ldc2:

[WebDrake]

Hmm, this is weird, my force-pushed branch changes aren't showing up. :-\

[WebDrake]

... and now they are. GitHub hooks running slowly, I guess.

[WebDrake]

@kinke @JohanEngelen any feedback on this? Just checking in, since it involves licensing ;-)

I'll submit a similar PR upstream once I have your OK on the changes here.

[JohanEngelen]

LGTM, thanks for upstreaming this to LDC!

[WebDrake]

LGTM, thanks for upstreaming this to LDC!

I'll try to do that tomorrow if I get a free moment :-)