Fixed ModuleInfo generation to no longer use the ModuleInfo class' default initializer for types/defaults, it's unsafe as initializers don't necesarily match the "formal" type. There might be explicit padding.

Changed -g switch to emit DW_LANG_D debug info, make demangling work with a patched GDB, still more work to do for full support of D's Dwarf extensions.
Added getNullValue helper method.

gen/tollvm.cpp

@@ -673,6 +673,11 @@ llvm::ConstantPointerNull* getNullPtr(const LLType* t)
     return llvm::ConstantPointerNull::get(pt);
 }
 
+LLConstant* getNullValue(const LLType* t)
+{
+    return LLConstant::getNullValue(t);
+}
+
 //////////////////////////////////////////////////////////////////////////////////////////
 
 size_t getTypeBitSize(const LLType* t)