[iOS/GN] Fix compilation of "all" with gn.

mojo/edk/system/BUILD.gn

Index: mojo/edk/system/BUILD.gn
diff --git a/mojo/edk/system/BUILD.gn b/mojo/edk/system/BUILD.gn
index ed5609a4f8bd3df316779db1d59169235f3dcaa1..daf93e475472da881c57be7d273e63013d35a29d 100644
--- a/mojo/edk/system/BUILD.gn
+++ b/mojo/edk/system/BUILD.gn
@@ -159,7 +159,6 @@ test("mojo_system_unittests") {
     "message_pipe_unittest.cc",
     "options_validation_unittest.cc",
     "platform_handle_dispatcher_unittest.cc",
-    "platform_wrapper_unittest.cc",
     "shared_buffer_dispatcher_unittest.cc",
     "shared_buffer_unittest.cc",
     "wait_set_dispatcher_unittest.cc",
@@ -173,6 +172,7 @@ test("mojo_system_unittests") {
     sources += [
       "data_pipe_unittest.cc",
       "multiprocess_message_pipe_unittest.cc",
+      "platform_wrapper_unittest.cc",
     ]
   }