support bazel complie this project and format code.

basic_content/extern/extern_c++/BUILD

@@ -0,0 +1,15 @@
+# please run `bazel run basic_content/extern/extern_c++:main`
+load("@rules_cc//cc:defs.bzl", "cc_binary", "cc_library")
+
+cc_library(
+    name = "add",
+    srcs = ["add.c"],
+    hdrs = ["add.h"],
+)
+
+cc_binary(
+    name = "main",
+    srcs = ["add.cpp"],
+    deps = [":add"],
+    copts = ["-std=c++11"]
+)