OpenMP support

[Scorn]

I too wonder how much work it would be to support OpenMP in gdc. From
http://www.drdobbs.com/high-performance-computing/226300277 it seems to be that
there is also quite a lot of magic on the compiler side (but which could already
be in the gcc parts). Maybe a concurrent garbage collector would also be needed
(Leandro Lucarella worked on this for his diploma thesis).

I hope someone can help to clear this up. If not OpenMP then at least a better
support for multicore programming in one way or another will be really important
for the future of D.