miri: fail when calling a function that requires an unavailable target feature miri will report an UB when calling a function that has a `#[target_feature(enable = ...)]` attribute is called and the required feature is not available. "Available features" are the same that `is_x86_feature_detected!` (or equivalent) reports to be available during miri execution (which can be enabled or disabled with the `-C target-feature` flag).