Add filegroup for sigchainlib version scripts

The sigchainlib version scripts are used by app_process, export
them as filegroups.

Test: m app_process
Change-Id: I536592afbaa98bf1e06cfb86f478ef5d612430cb
diff --git a/sigchainlib/Android.bp b/sigchainlib/Android.bp
index 5f055ec..3209478 100644
--- a/sigchainlib/Android.bp
+++ b/sigchainlib/Android.bp
@@ -62,3 +62,13 @@
     srcs: ["sigchain_test.cc"],
     whole_static_libs: ["libsigchain"],
 }
+
+filegroup {
+    name: "art_sigchain_version_script32.txt",
+    srcs: ["version-script32.txt"],
+}
+
+filegroup {
+    name: "art_sigchain_version_script64.txt",
+    srcs: ["version-script64.txt"],
+}