LDC 1.15.0-beta1

[kinke]

Glad to announce the first beta for LDC 1.15:

* Based on D 2.085.0.
* Support for LLVM 8.0. The prebuilt packages ship with LLVM 
8.0.0-rc4 and include the Khronos SPIRV-LLVM-Translator, so that 
dcompute can now emit OpenCL too.
* New -lowmem switch to enable the GC for the front-end, trading 
compile times for less required memory (in some cases, by more 
than 60%).
* Dropped support for 32-bit macOS. Min macOS version for 
prebuilt package raised to 10.9.
* Fix: functions annotated with `pragma(inline, true)` are 
implicitly cross-module-inlined again.

Full release log and downloads: 
https://github.com/ldc-developers/ldc/releases/tag/v1.15.0-beta1

Please help test, and thanks to all contributors!