implement noinline

https://github.com/ziglang/zig/blob/6d691d3540b1979f0a8d604922c93209b9c0dba0/src/AstGen.zig#L3364

```zig
noinline fn foo() void {}
```

If you look at the ZIR, the "noinline" information is lost.