llvm-context: lazy handling of function arguments and immutable data (#282)

- Lazily load function arguments so that they can be passed as pointers.
- Lazily call the immutable store function to avoid storing zero sized
immutable data.

---------

Signed-off-by: Cyrill Leutwiler <bigcyrill@hotmail.com>

crates/solidity/src/yul/parser/statement/assignment.rs

@@ -139,13 +139,14 @@ where
                         identifier.inner,
                     )
                 })?;
-            context.build_store(pointer, value.to_llvm())?;
+            context.build_store(pointer, value.access(context)?)?;
             return Ok(());
         }
 
-        let llvm_type = value.to_llvm().into_struct_value().get_type();
+        let value = value.access(context)?;
+        let llvm_type = value.into_struct_value().get_type();
         let tuple_pointer = context.build_alloca(llvm_type, "assignment_pointer");
-        context.build_store(tuple_pointer, value.to_llvm())?;
+        context.build_store(tuple_pointer, value)?;
 
         for (index, binding) in self.bindings.into_iter().enumerate() {
             context.set_debug_location(self.location.line, 0, None)?;