support bazel complie this project and format code.

learn_class/modern_cpp_30/memorymodel_atomic/hungrysingleton.cpp

@@ -0,0 +1,17 @@
+//
+// Created by light on 20-2-6.
+//
+
+class singleton {
+private:
+    singleton() {}
+    static singleton *p;
+public:
+    static singleton *instance();
+};
+
+singleton *singleton::p = new singleton();
+singleton* singleton::instance() {
+    return p;
+}
+