- Fixed LLVM style CL args for D2.

- Moved main() into its own file gen/main.cpp
- Fixed basic cross compilation
- removed the option for setting OS
- added support for llc's mattr, mcpu and mtriple switches
- added basic ABI abstraction for return value rewrites, it's not perfect and will probably be completely rewritten once I get to handling parameter rewrites as well.
- x86-64 extern(C) abi for cfloat returns now match (llvm-)gcc.

gen/tollvm.cpp

@@ -28,13 +28,6 @@ bool DtoIsPassedByRef(Type* type)
     return (t == Tstruct || t == Tsarray);
 }
 
-bool DtoIsReturnedInArg(Type* type)
-{
-    Type* typ = type->toBasetype();
-    TY t = typ->ty;
-    return (t == Tstruct || t == Tsarray);
-}
-
 unsigned DtoShouldExtend(Type* type)
 {
     type = type->toBasetype();