LDC 1.18.0-beta1

[kinke]

Glad to announce the first beta for LDC 1.18:

* Based on D 2.088.0+ (yesterday's stable).
* Bundled dub upgraded to v1.17.0+ with improved LDC support, 
incl. cross-compilation.
* Init symbols of zero-initialized structs are no longer emitted.
* druntime: DMD-compatible {load,store}Unaligned and prefetch 
added to core.simd.
* JIT improvements, incl. multi-threaded compilation.

Full release log and downloads: 
https://github.com/ldc-developers/ldc/releases/tag/v1.18.0-beta1

Please help test, and thanks to all contributors!