fix(frontend): 补充不支持语法的警告输出

src/irgen/IRGenDecl.cpp

@@ -28,7 +28,7 @@ void IRGenImpl::GenBlock(const ast::Block& block) {
 void IRGenImpl::GenVarDecl(const ast::VarDecl& decl) {
   auto it = locals_.find(decl.name);
   if (it == locals_.end()) {
-    throw std::runtime_error("变量栈槽未创建: " + decl.name);
+    throw std::runtime_error("[irgen] 变量栈槽未创建: " + decl.name);
   }
 
   ir::Value* init = nullptr;

src/irgen/IRGenExp.cpp

@@ -16,7 +16,7 @@ ir::Value* IRGenImpl::GenExpr(const ast::Expr& expr) {
   if (auto var = dynamic_cast<const ast::VarExpr*>(&expr)) {
     auto it = locals_.find(var->name);
     if (it == locals_.end()) {
-      throw std::runtime_error("变量未找到: " + var->name);
+      throw std::runtime_error("[irgen] 变量未找到: " + var->name);
     }
     std::string name = ir::DefaultContext().NextTemp();
     return builder_.CreateLoad(it->second, name);
@@ -33,5 +33,5 @@ ir::Value* IRGenImpl::GenExpr(const ast::Expr& expr) {
       return builder_.CreateBinary(ir::Opcode::Add, lhs, rhs, name);
     }
   }
-  throw std::runtime_error("不支持的表达式类型");
+  throw std::runtime_error("[irgen] 暂不支持的表达式类型");
 }

src/irgen/IRGenFunc.cpp

@@ -16,7 +16,7 @@ IRGenImpl::IRGenImpl(ir::Module& module)
 
 void IRGenImpl::Gen(const ast::CompUnit& ast) {
   if (!ast.func || !ast.func->body) {
-    throw std::runtime_error("AST 不完整：缺少 main 定义");
+    throw std::runtime_error("[irgen] AST 不完整：缺少 main 定义");
   }
   GenBlock(*ast.func->body);
 }

src/irgen/IRGenStmt.cpp

@@ -15,5 +15,5 @@ void IRGenImpl::GenStmt(const ast::Stmt& stmt) {
     builder_.CreateRet(v);
     return;
   }
-  throw std::runtime_error("不支持的语句类型");
+  throw std::runtime_error("[irgen] 暂不支持的语句类型");
 }