use a trampoline to get to the spicy _x functions

internal/msgx/msgx_ios.go

@@ -0,0 +1,12 @@
+package msgx
+
+import "syscall"
+
+// Available is always false on iOS, so App Store builds never look up private symbols.
+func Available() bool { return false }
+
+// Send always returns ENOSYS on iOS.
+func Send(uintptr, []Hdr, int) (int, syscall.Errno) { return 0, syscall.ENOSYS }
+
+// Recv always returns ENOSYS on iOS.
+func Recv(uintptr, []Hdr, int) (int, syscall.Errno) { return 0, syscall.ENOSYS }