LDC 1.8.0-beta1

[kinke]

Hi everyone,

on behalf of the LDC team, I'm glad to announce the first beta 
for LDC 1.8. The highlights of this version in a nutshell:

* Based on D 2.078.3.
* New switch `-link-defaultlib-shared` to link against shared 
druntime/Phobos.
* Plugins support, compatible with existing Clang plugins.
* Support for LLVM IR-based PGO as alternative to existing 
(AST-based) PGO.
* Basic support for LLVM XRay instrumentation.

Full release log and downloads: 
https://github.com/ldc-developers/ldc/releases/tag/v1.8.0-beta1

Thanks to all contributors!