Fix the same $ procedure argument generating duplicate instantiations

src/checker.cpp

@@ -2153,7 +2153,9 @@ gb_internal void add_entity_use(CheckerContext *c, Ast *identifier, Entity *enti
 	if (identifier == nullptr || identifier->kind != Ast_Ident) {
 		return;
 	}
-	entity->identifier.store(identifier);
+	// NOTE: only set it once, as `$` procedure arguments are matched by this identifier
+	Ast *empty_ident = nullptr;
+	entity->identifier.compare_exchange_strong(empty_ident, identifier);
 
 	identifier->Ident.entity = entity;