./x check std --target aarch64-apple-ios fails when cross-checking due to missing xcrun

[ChrisDenton]

On a non-mac host, checking std for an ios target fails with the following error:

> ./x check std --target aarch64-apple-ios                                                                                                                          
Building bootstrap
    Finished `dev` profile [unoptimized] target(s) in 0.8s


error occurred: Failed to find tool. Is `xcrun` installed? (see https://docs.rs/cc/latest/cc/#compile-time-requirements for help)


Build completed unsuccessfully in 0:00:01

Ideally I should be able to check any target from any host.

[onur-ozkan]

Previously, this was resolved in #128871 but then check step had to be excluded due to unexpected rebuild issues (see #130108). Let's keep this issue open until we find a solution that prevents rebuilds and ignores the linker configuration for check step.