Open MPI with D

[Andrej Mitrovic]

There's an edge-case here to be aware of, if you don't reference the
symbol there won't be linker errors (at least with optlink, and this
makes sense when you think about it):

// no linker errors
extern extern(C) int x;
void main() { }

// linker errors
extern extern(C) int x;
void main() { int z = x; }