[dmd-internals] x86 fiber_switchContext

[Iain Buclaw]

Hi,

I mentioned this a while back, and don't recall any other response
except from Martin on this.  I'd like to drop the ucontext
implementation in the Fiber implementation and move the inline asm
into threadasm.S so everyone benefits.

This is one of the blockers for gdc on Mac/OSX for instance, and a
slimmed down size of Fiber for gdc on GNU/Linux would be ideal - along
with removing the current modifications we make to thread.d/thread.di
to make the static asserts pass.

Regards
Iain