Add run-pass test and fix failing test

Author: camelid

src/test/ui/parser/inline-const-pat-let.rs

@@ -0,0 +1,30 @@
+// run-pass
+
+#![allow(incomplete_features)]
+#![feature(inline_const)]
+
+fn if_let_1() -> i32 {
+    let x = 2;
+    const Y: i32 = 3;
+
+    if let const { (Y + 1) / 2 } = x {
+        x
+    } else {
+        0
+    }
+}
+
+fn if_let_2() -> i32 {
+    let x = 2;
+
+    if let const { 1 + 2 } = x {
+        const { 1 + 2 }
+    } else {
+        0
+    }
+}
+
+fn main() {
+    assert_eq!(if_let_1(), 2);
+    assert_eq!(if_let_2(), 0);
+}

src/test/ui/parser/keyword-const-as-identifier.rs

@@ -1,5 +1,3 @@
-// This file was auto-generated using 'src/etc/generate-keyword-tests.py const'
-
 fn main() {
-    let const = "foo"; //~ error: expected identifier, found keyword `const`
+    let const = "foo"; //~ ERROR expected `{`, found `=`
 }

src/test/ui/parser/keyword-const-as-identifier.stderr

@@ -1,5 +1,5 @@
 error: expected `{`, found `=`
-  --> $DIR/keyword-const-as-identifier.rs:4:15
+  --> $DIR/keyword-const-as-identifier.rs:2:15
    |
 LL |     let const = "foo";
    |               ^ expected `{`