Mostly rewrite debug info generation in terms of llvm/Analysis/DebugInfo.h.

Add getCompilationModule to Dsymbol and fix template compile unit decision code.
Runtime compiles with -g again.

ir/irfunction.cpp

@@ -31,8 +31,6 @@ IrFunction::IrFunction(FuncDeclaration* fd)
     _arguments = NULL;
     _argptr = NULL;
     
-    dwarfSubProg = NULL;
-
     nextUnique.push(0);
 }