Platform-dependent tests for druntime

[Ali Çehreli]

Since I don't have access to Windows, OS X, etc. systems nor have I 
expertise in them, I don't trust myself to write core.thread tests for 
anything but Posix.

What to do for non-Posix systems? I'm tempted to wrap the entire test 
code with version(Posix) but it will give the wrong impression that the 
code passes for all other systems as well. For example, inside
druntime/test/thread/src/attach_detach.d I can do this:

version (Posix) {
     // Real test ...
} else {
     void main() {}    // Deceptive code
}

How can I seek testers for a pull request that I'm ready to post? Post 
PR, hopefully get merged, and then open issues for platforms that don't 
have those tests?

It would be easier if test/thread/Makefile had a way of running 
platform-specific tests. Yes, probably I'm volunteering but again, I 
couldn't do much without other platforms.

I have a feeling our automated test harness already has such machines. 
If so, where are they? :)

Ali