LDC 1.39.0-beta1

[kinke]

Glad to announce the first beta for LDC 1.39. Major changes:

* Based on D 2.109.0.
* LLVM for prebuilt packages bumped to v18.1.6.
* Support for LLVM 11-14 was dropped. The CLI options 
`-passmanager` and `-opaque-pointers` were removed.

Full release log and downloads: 
https://github.com/ldc-developers/ldc/releases/tag/v1.39.0-beta1

Please help test, and thanks to all contributors & sponsors!