add a test

Author: RalfJung

src/test/ui/consts/extra-const-ub/issue-101034.rs

@@ -0,0 +1,17 @@
+// check-pass
+// compile-flags: -Zextra-const-ub-checks
+
+#[repr(packed)]
+pub struct Foo {
+    bar: u8,
+    baa: [u32; 1],
+}
+
+const FOOMP: Foo = Foo {
+    bar: 0,
+    baa: [69; 1],
+};
+
+fn main() {
+    let _val = FOOMP;
+}