Open-source Bazel integration tests

It is a first batch of integration tests for Bazel. They tests some
basic behaviors and nominal cases of Bazel rules (especially they tests
the behavior of the examples provided in //examples).

--
MOS_MIGRATED_REVID=89440074
diff --git a/examples/cpp/BUILD b/examples/cpp/BUILD
index 195bbb3..7c0543e 100644
--- a/examples/cpp/BUILD
+++ b/examples/cpp/BUILD
@@ -23,3 +23,11 @@
     srcs = ["hello-fail.cc"],
     deps = [":hello-lib"],
 )
+
+filegroup(
+    name = "srcs",
+    srcs = ["BUILD"] + glob([
+        "**/*.cc",
+        "**/*.h",
+    ]),
+)