Rollup merge of #145932 - JamieCunliffe:target-feature-inlining, r=jackh726

Allow `inline(always)` with a target feature behind a unstable feature `target_feature_inline_always`.

Rather than adding the inline always attribute to the function definition, we add it to the callsite. We can then check that the target features match and that the call would be safe to inline. If the function isn't inlined due to a mismatch, we emit a warning informing the user that the function can't be inlined due to the target feature mismatch.

See tracking issue rust-lang/rust#145574

Author: Zalathar