Add a regression test for rust-lang#64173 and rust-lang#66152

Author: JohnTitor

src/test/ui/lifetimes/issue-64173-unused-lifetimes.rs

@@ -0,0 +1,19 @@
+use std::mem::size_of;
+
+struct Foo<'s> { //~ ERROR: parameter `'s` is never used
+    array: [(); size_of::<&Self>()],
+    //~^ ERROR: generic `Self` types are currently not permitted in anonymous constants
+}
+
+// The below is taken from https://github.com/rust-lang/rust/issues/66152#issuecomment-550275017
+// as the root cause seems the same.
+
+const fn foo<T>() -> usize {
+    0
+}
+
+struct Bar<'a> { //~ ERROR: parameter `'a` is never used
+    beta: [(); foo::<&'a ()>()], //~ ERROR: a non-static lifetime is not allowed in a `const`
+}
+
+fn main() {}

src/test/ui/lifetimes/issue-64173-unused-lifetimes.stderr

@@ -0,0 +1,35 @@
+error[E0658]: a non-static lifetime is not allowed in a `const`
+  --> $DIR/issue-64173-unused-lifetimes.rs:16:23
+   |
+LL |     beta: [(); foo::<&'a ()>()],
+   |                       ^^
+   |
+   = note: see issue #76560 <https://github.com/rust-lang/rust/issues/76560> for more information
+   = help: add `#![feature(generic_const_exprs)]` to the crate attributes to enable
+
+error: generic `Self` types are currently not permitted in anonymous constants
+  --> $DIR/issue-64173-unused-lifetimes.rs:4:28
+   |
+LL |     array: [(); size_of::<&Self>()],
+   |                            ^^^^
+
+error[E0392]: parameter `'s` is never used
+  --> $DIR/issue-64173-unused-lifetimes.rs:3:12
+   |
+LL | struct Foo<'s> {
+   |            ^^ unused parameter
+   |
+   = help: consider removing `'s`, referring to it in a field, or using a marker such as `PhantomData`
+
+error[E0392]: parameter `'a` is never used
+  --> $DIR/issue-64173-unused-lifetimes.rs:15:12
+   |
+LL | struct Bar<'a> {
+   |            ^^ unused parameter
+   |
+   = help: consider removing `'a`, referring to it in a field, or using a marker such as `PhantomData`
+
+error: aborting due to 4 previous errors
+
+Some errors have detailed explanations: E0392, E0658.
+For more information about an error, try `rustc --explain E0392`.