Auto merge of #56833 - nagisa:ios-fix, r=alexcrichton
Auto merge of #56833 - nagisa:ios-fix, r=alexcrichton

Provide -isysroot with sdkroot for ios builds

Necessary for the new XCode?

Absolutely positively definitely untested… although I did

```
cargo rustc -- -Clink-arg=-isysroot -Clink-arg=$sdk_root
```

and stuff did compile for once.

graydon/rust,aidancully/rust,GBGamer/rust,graydon/rust,graydon/rust,GBGamer/rust,graydon/rust,graydon/rust,aidancully/rust,GBGamer/rust,GBGamer/rust,graydon/rust,aidancully/rust,aidancully/rust,GBGamer/rust,GBGamer/rust,aidancully/rust,GBGamer/rust,aidancully/rust,GBGamer/rust