Add a bazel-srcs target to the top-level package containing all Bazel sources

This target include all non tests targets of Bazel to do integration tests of
bootstrapping.

--
MOS_MIGRATED_REVID=115830741
diff --git a/scripts/BUILD b/scripts/BUILD
index cc4d157..26aab55 100644
--- a/scripts/BUILD
+++ b/scripts/BUILD
@@ -31,3 +31,9 @@
         "//src/test/shell:bashunit",
     ],
 )
+
+filegroup(
+    name = "srcs",
+    srcs = glob(["**"]),
+    visibility = ["//:__pkg__"],
+)