Warned at making precompiled header on mswin.

```
building rb_mjit_header-2.7.0.pch
vm.c
d:\a\ruby\ruby\src\vm_args.c(1117): warning C4047: '=': 'const rb_callable_method_entry_t *' differs in levels of indirection from 'int'
rb_mjit_header-2.7.0.pch updated
```