Add all the sources to //:srcs filegroup and add a check to detect
missing file to it.

We need to activate this check on presubmits

--
Change-Id: Ia95e92d3816ce92bb69bc0e2cf56e9c60b68d970
Reviewed-on: https://bazel-review.googlesource.com/#/c/3949/
MOS_MIGRATED_REVID=126404792
diff --git a/scripts/BUILD b/scripts/BUILD
index 26aab55..398ce4c 100644
--- a/scripts/BUILD
+++ b/scripts/BUILD
@@ -34,6 +34,9 @@
 
 filegroup(
     name = "srcs",
-    srcs = glob(["**"]),
+    srcs = glob(["**"]) + [
+        "//scripts/release:srcs",
+        "//scripts/packages:srcs",
+    ],
     visibility = ["//:__pkg__"],
 )