Update and add new test (fixes rust-lang#55353)

Author: oli-obk

src/test/ui/consts/dangling-alloc-id-ice.rs

@@ -7,7 +7,7 @@ union Foo<'a> {
     long_live_the_unit: &'static (),
 }
 
-const FOO: &() = { //~ ERROR this constant cannot be used
+const FOO: &() = { //~ ERROR any use of this value will cause an error
     let y = ();
     unsafe { Foo { y: &y }.long_live_the_unit }
 };

src/test/ui/consts/dangling-alloc-id-ice.stderr

@@ -1,7 +1,7 @@
-error: this constant cannot be used
+error: any use of this value will cause an error
   --> $DIR/dangling-alloc-id-ice.rs:10:1
    |
-LL | / const FOO: &() = { //~ ERROR this constant cannot be used
+LL | / const FOO: &() = { //~ ERROR any use of this value will cause an error
 LL | |     let y = ();
 LL | |     unsafe { Foo { y: &y }.long_live_the_unit }
 LL | | };

src/test/ui/consts/dangling_raw_ptr.rs

@@ -0,0 +1,10 @@
+#![feature(const_let)]
+
+const FOO: *const u32 = { //~ ERROR any use of this value will cause an error
+    let x = 42;
+    &x
+};
+
+fn main() {
+    let x = FOO;
+}

src/test/ui/consts/dangling_raw_ptr.stderr

@@ -0,0 +1,13 @@
+error: any use of this value will cause an error
+  --> $DIR/dangling_raw_ptr.rs:3:1
+   |
+LL | / const FOO: *const u32 = { //~ ERROR any use of this value will cause an error
+LL | |     let x = 42;
+LL | |     &x
+LL | | };
+   | |__^ type validation failed: encountered dangling pointer in final constant
+   |
+   = note: #[deny(const_err)] on by default
+
+error: aborting due to previous error
+