Merge with 2.065 pre-release development

It's a round-about time we start to get this done.

This merges the D-frontend up until https://github.com/D-Programming-Language/dmd/commit/d098e5caafd7a1bc8115870a6449c77d61d0d9fd

From here on afterwards @yebblies gets quite prolific in his changes, and it's hard to keep a track of anything that is going on.

Things on the TODO list before 2.065 merge is complete:
- Rename glue sources using the new proposed scheme.
- Rewrite ``d-toir.cc`` as a visitor
- Remove ``dfrontend/builtins.c`` and re-implement in the glue.
- Maybe migrate D intrinsics and library routines to a ``.def`` file.
- Maybe remove ``dfrontend/cppmangle.c`` and integrate in the glue layer.

So, only a couple thousand LOC to write. ;o)