Add regression test

Author: oli-obk

Diff for: tests/ui/inline-const/const_block_pat_liveness.rs

@@ -0,0 +1,18 @@
+//! This test used to ICE because const blocks didn't have a body
+//! anymore, making a lot of logic very fragile around handling the
+//! HIR of a const block.
+//! https://github.com/rust-lang/rust/issues/125846
+
+//@ check-pass
+
+#![feature(inline_const_pat)]
+
+fn main() {
+    match 0 {
+        const {
+            let a = 10_usize;
+            *&a
+        }
+        | _ => {}
+    }
+}