Add missing clobbers to context switching

This only shows in release mode, the compiler tries to preserve some
value in rdi, but that gets replaced inside the fiber. This would not
happen in the C calling convention, but in these normal Zig functions,
it can happen.

lib/std/Io/EventLoop.zig

@@ -644,6 +644,7 @@ inline fn contextSwitch(message: *const SwitchMessage) *const SwitchMessage {
             : [received_message] "={x1}" (-> *const @FieldType(SwitchMessage, "contexts")),
             : [message_to_send] "{x1}" (&message.contexts),
             : .{
+              .x0 = true,
               .x1 = true,
               .x2 = true,
               .x3 = true,
@@ -745,6 +746,7 @@ inline fn contextSwitch(message: *const SwitchMessage) *const SwitchMessage {
               .rdx = true,
               .rbx = true,
               .rsi = true,
+              .rdi = true,
               .r8 = true,
               .r9 = true,
               .r10 = true,