Propagate temporary lifetime extension into if and match. This PR makes this work: ```rust let a = if true { ..; &temp() // used to error, but now gets lifetime extended } else { ..; &temp() // used to error, but now gets lifetime extended }; ``` and ```rust let a = match () { _ => { ..; &temp() // used to error, but now gets lifetime extended } }; ``` to make it consistent with: ```rust let a = { ..; &temp() // lifetime is extended }; ``` This is one small part of [the temporary lifetimes work](https://github.com/rust-lang/lang-team/issues/253). This part is backwards compatible (so doesn't need be edition-gated), because all code affected by this change previously resulted in a hard error.