Add libsigchain as dependency of platform.

Test: m and boot
Test: atest CtsJniTestCases
Bug: 142944043
Change-Id: Iefded35c478d6278c56fbfa02e5cb364a9326c5c

rootdir/etc/linker.config.json

@@ -6,6 +6,7 @@
     "libnativebridge.so",
     "libnativehelper.so",
     "libnativeloader.so",
+    "libsigchain.so",
     "libandroidicu.so",
     "libicu.so",
     // TODO(b/122876336): Remove libpac.so once it's migrated to Webview
@@ -26,4 +27,4 @@
     "libadb_pairing_connection.so",
     "libadb_pairing_server.so"
   ]
-}
+}