Update to LDC 1.15.0 stable release, incl. LLVM 8.0.0

[kinke]

This is a dummy PR, just for making the 1.15 branch visible. Pinging @WebDrake.

[WebDrake]

Thanks for the patch. A couple of notes for future reference:

• the branch name actually matches what I use for the individual release branches which packages are built from

• I know it's just for testing, but we really shouldn't be submitting version upgrade PRs against the 1.14 branch!

What I would usually do is:

• create a 1.N+1 branch from the 1.N branch

• submit the version upgrade patch against the 1.N+1 branch

Anyway, per se this LGTM apart from one small thing -- wasn't there an extra build optimization that could be enabled with 1.15 ... ? I remember you mentioning it when recommending the bootstrap compiler be built from the same version as the release itself.

[kinke]

I know it's just for testing

Wouldn't even by necessary, all branches are tested too. It was just to make this visible to you. ;)

wasn't there an extra build optimization

Nope, but v1.15 as host compiler (with the GC improvements in its druntime) significantly increases the usefulness of the new -lowmem option, so we're already set.

[WebDrake]

Nope, but v1.15 as host compiler (with the GC improvements in its druntime) significantly increases the usefulness of the new -lowmem option, so we're already set.

So no extra build flags needed, the benefits are automatic?

[kinke]

Yes, just a better/less wasteful GC in druntime.

[WebDrake]

Awesome. In that case I'll close this PR and just set up the job to build this version. We can deal with the LLVM C++ flags issue in a separate PR.

[WebDrake]

Closing, as the branch should not be merged into 1.14.

[WebDrake]

Snap package definition in place: https://code.launchpad.net/~ldc-developers/+snap/ldc2-1.15