WebRTC's GN macros are about to get default visibility restrictions

In this CL: https://webrtc-review.googlesource.com/c/src/+/24140

Bug: webrtc:8254
Change-Id: I869609676979f6f4dcfb36a3eb1f0645720654fd
Reviewed-on: https://chromium-review.googlesource.com/778840Reviewed-by: Henrik Andreasson <henrika@chromium.org>
Commit-Queue: Karl Wiberg <kwiberg@chromium.org>
Cr-Commit-Position: refs/heads/master@{#524363}

third_party/libjingle_xmpp/BUILD.gn

@@ -17,6 +17,7 @@ config("libjingle_xmpp_common_config") {
 }
 
 rtc_static_library("rtc_task_runner") {
+  visibility = [ "*" ]
   sources = [
     "task_runner/task.cc",
     "task_runner/task.h",
@@ -28,6 +29,7 @@ rtc_static_library("rtc_task_runner") {
 }
 
 rtc_static_library("rtc_xmllite") {
+  visibility = [ "*" ]
   sources = [
     "xmllite/qname.cc",
     "xmllite/qname.h",
@@ -64,6 +66,7 @@ config("rtc_xmpp_warnings_config") {
 }
 
 rtc_static_library("rtc_xmpp") {
+  visibility = [ "*" ]
   cflags = []
   sources = [
     "xmpp/asyncsocket.h",