Some help with core/thread refactoring

[Stefanos Baziotis]

Hello everyone,

I have been trying to refactor core/thread (with the help of 
Nicholas Wilson).
PR: https://github.com/dlang/druntime/pull/2689

It seems it's something that the D community likes and I want to 
progress on this.

I get a failed test on AppVeyor and one on auto-tester.

Both are related to Windows.

-- On AppVeyor --

It says there's a unittest that fails in exception.d. Now:
- I can't find it in exception.d
- It seems unrelated to the PR but it's kind of persistent (it's 
the second time it appeared).

-- On auto-tester --

I get an error when try to build Windows:
std\concurrency.d(39): Error: module `thread` is in file 
'core\thread.d' which cannot be read.

Have I missed something on the .mak files or smth?

Also, I'm trying to compile DMD on Windows to compile druntime 
but it fails. I get an error like:
std.process.ProcessException at std\process.d(755): Failed to spawn 
new process

I don't know how to move forwards.