upb needs a patch to get rid of offsetof warnings

Index: third_party/upb/BUILD
--- third_party/upb/BUILD.orig
+++ third_party/upb/BUILD
@@ -22,4 +22,8 @@ filegroup(
     visibility = ["//third_party:__pkg__"],
 )
 
+exports_files([
+    "upb.patch",
+])
+
 package(default_visibility = ["//visibility:public"])
