Introduce if-let guards in the HIR

src/test/ui/rfc-2294-if-let-guard/feature-gate.rs

@@ -6,7 +6,6 @@ fn _if_let_guard() {
     match () {
         () if let 0 = 1 => {}
         //~^ ERROR `if let` guard is not implemented
-        //~| ERROR `let` expressions are not supported here
 
         () if (let 0 = 1) => {}
         //~^ ERROR `let` expressions in this position are experimental

src/test/ui/rfc-2294-if-let-guard/feature-gate.stderr

@@ -169,15 +169,6 @@ LL |     use_expr!((let 0 = 1));
    = note: see issue #53667 <https://github.com/rust-lang/rust/issues/53667> for more information
    = help: add `#![feature(let_chains)]` to the crate attributes to enable
 
-error: `let` expressions are not supported here
-  --> $DIR/feature-gate.rs:7:15
-   |
-LL |         () if let 0 = 1 => {}
-   |               ^^^^^^^^^
-   |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
-   = note: as well as when nested within `&&` and parenthesis in those conditions
-
 error: `let` expressions are not supported here
   --> $DIR/feature-gate.rs:11:16
    |