Add D front-end, libphobos library, and D2 testsuite... to GCC

[Mike Parker]

Congratulations are in order for Iain Buclaw. His efforts have 
been rewarded in a big way. Last Friday, he got the greenlight to 
move forward with submitting his changes into GCC:

https://gcc.gnu.org/ml/gcc-patches/2018-10/msg01676.html

That's now a reality.

https://gcc.gnu.org/git/?p=gcc.git;a=commit;h=03385ed3d679cd8125f282697a1c7cf46f8361cc

Hopefully around the time of DConf next year we'll see GDC 
included with the release of GCC 9. How cool is that?