- 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/irstate.cpp

@@ -16,7 +16,9 @@
 #include "tollvm.h"
 
 IRState* gIR = 0;
+llvm::TargetMachine* gTargetMachine = 0;
 const llvm::TargetData* gTargetData = 0;
+TargetABI* gABI = 0;
 
 //////////////////////////////////////////////////////////////////////////////////////////
 IRScope::IRScope()