Fix test tail with mjit options for clang provided by Xcode 16

```
clang: error: unknown argument '-emit-pch'; did you mean '-Xclang -emit-pch'?
MJIT warning: Making precompiled header failed on compilation. Stopping MJIT worker...
Successful MJIT finish
```

mjit_worker.c

@@ -870,6 +870,7 @@ make_pch(void)
 {
     const char *rest_args[] = {
 # ifdef __clang__
+        "-Xclang",
         "-emit-pch",
         "-c",
 # endif