Add known-bug tests for a few I-unsound issues

tests/ui/codegen/issue-107975-pointer-inequality.rs

@@ -0,0 +1,17 @@
+// run-pass
+// known-bug: #107975
+fn main() {
+    let a: *const u8;
+    let b: *const u8;
+    {
+        let v: [u8; 16] = [core::hint::black_box(0); 16];
+        a = &(v[0]);
+    }
+    {
+        let v: [u8; 16] = [core::hint::black_box(0); 16];
+        b = &(v[0]);
+    }
+    assert_ne!(a, b);
+    println!("{a:?} {b:?}");
+    assert_eq!(a, b);
+}

tests/ui/specialization/issue-105787.rs

@@ -0,0 +1,39 @@
+// check-pass
+// known-bug: #105787
+trait ToUnit<'a> {
+    type Unit;
+}
+
+struct LocalTy;
+impl<'a> ToUnit<'a> for *const LocalTy {
+    type Unit = ();
+}
+
+impl<'a, T: Copy + ?Sized> ToUnit<'a> for *const T {
+    type Unit = ();
+}
+
+trait Overlap<T> {
+    type Assoc;
+}
+
+type Assoc<'a, T> = <*const T as ToUnit<'a>>::Unit;
+
+impl<T> Overlap<T> for T {
+    type Assoc = usize;
+}
+
+impl<T> Overlap<for<'a> fn(&'a (), Assoc<'a, T>)> for T
+where
+    for<'a> *const T: ToUnit<'a>,
+{
+    type Assoc = Box<usize>;
+}
+
+fn foo<T: Overlap<U>, U>(x: T::Assoc) -> T::Assoc {
+    x
+}
+
+fn main() {
+    foo::<for<'a> fn(&'a (), ()), for<'a> fn(&'a (), ())>(3usize);
+}

tests/ui/type-alias-impl-trait/issue-108425-impl-generics-unsoundness.rs

@@ -0,0 +1,25 @@
+// known-bug: #108425
+// check-pass
+#![feature(type_alias_impl_trait)]
+use std::fmt::Display;
+
+type Opaque<'a> = impl Sized + 'static;
+fn define<'a>() -> Opaque<'a> {}
+
+trait Trait {
+    type Assoc: Display;
+}
+impl<'a> Trait for Opaque<'a> {
+    type Assoc = &'a str;
+}
+
+// ======= Exploit =======
+
+fn extend<T: Trait + 'static>(s: T::Assoc) -> Box<dyn Display> {
+    Box::new(s)
+}
+
+fn main() {
+    let val = extend::<Opaque<'_>>(&String::from("blah blah blah"));
+    println!("{}", val);
+}