Add regression test

Author: oli-obk

tests/ui/inline-const/promotion.rs

@@ -0,0 +1,21 @@
+#![feature(inline_const)]
+#![allow(arithmetic_overflow, unconditional_panic)]
+// check-pass
+
+// The only way to have promoteds that fail is in `const fn` called from `const`/`static`.
+const fn div_by_zero() -> i32 {
+    1 / 0
+}
+
+const fn mk_false() -> bool {
+    false
+}
+
+fn main() {
+    let v = const {
+        if mk_false() {
+            let _x: &'static i32 = &div_by_zero();
+        }
+        42
+    };
+}