selfhost: introduce using-based imports for compiler/parser/tools; keep includes temporarily. llvm: add PHI wiring JSON trace + unit/integration tests; fast test suite extended. runner: split selfhost helpers, small cleanups.

src/mir/loop_builder.rs

@@ -318,6 +318,7 @@ impl<'a> LoopBuilder<'a> {
         }
     }
 
+    #[allow(dead_code)]
     fn add_predecessor(&mut self, block: BasicBlockId, pred: BasicBlockId) -> Result<(), String> {
         if let Some(ref mut function) = self.parent_builder.current_function {
             if let Some(block) = function.get_block_mut(block) {