Conditional compilation inside asm and enum declarations

[Walter Bright]

Andrei Alexandrescu wrote:
> Then I have the function right there with all versioned implementations. 
> To me that seems better than Phobos' existing style of version'ing large 
> portions of code, which inevitably results in duplicating a lot of the 
> functionality in two places.

I wouldn't consider Phobos to be an exemplary example of how to do 
versioning, though it should be. I think much of it, like std.file, 
should be split off into os-dependent "personality" modules, much like 
the os api modules have been.