tests: move crashes/79409.rs to ui suite

This test no longer crashes the compiler as `Box` no longer accepts
`PointeeSized`-types. It eventually could, but not because of
`Deref::Target` currently, so this doesn't fail anymore and there wasn't
an obvious to add new types to make it continue to fail because `Deref`
is special.

Author: davidtwco

tests/crashes/79409.rs

@@ -0,0 +1,21 @@
+#![feature(extern_types)]
+#![feature(unsized_locals)]
+//~^ WARN the feature `unsized_locals` is incomplete
+
+// Regression test for #79409
+
+extern "C" {
+    type Device;
+}
+
+unsafe fn make_device() -> Box<Device> {
+//~^ ERROR the size for values of type `Device` cannot be known
+    Box::from_raw(0 as *mut _)
+//~^ ERROR the size for values of type `Device` cannot be known
+//~| ERROR the size for values of type `Device` cannot be known
+}
+
+fn main() {
+    let d: Device = unsafe { *make_device() };
+//~^ ERROR the size for values of type `Device` cannot be known
+}

tests/ui/extern/extern-types-unsizing-79409.rs

@@ -0,0 +1,60 @@
+warning: the feature `unsized_locals` is incomplete and may not be safe to use and/or cause compiler crashes
+  --> $DIR/extern-types-unsizing-79409.rs:2:12
+   |
+LL | #![feature(unsized_locals)]
+   |            ^^^^^^^^^^^^^^
+   |
+   = note: see issue #48055 <https://github.com/rust-lang/rust/issues/48055> for more information
+   = note: `#[warn(incomplete_features)]` on by default
+
+error[E0277]: the size for values of type `Device` cannot be known
+  --> $DIR/extern-types-unsizing-79409.rs:11:28
+   |
+LL | unsafe fn make_device() -> Box<Device> {
+   |                            ^^^^^^^^^^^ doesn't have a known size
+   |
+   = help: the trait `MetaSized` is not implemented for `Device`
+note: required by a bound in `Box`
+  --> $SRC_DIR/alloc/src/boxed.rs:LL:COL
+
+error[E0277]: the size for values of type `Device` cannot be known
+  --> $DIR/extern-types-unsizing-79409.rs:13:19
+   |
+LL |     Box::from_raw(0 as *mut _)
+   |     ------------- ^^^^^^^^^^^ the trait `MetaSized` is not implemented for `Device`
+   |     |
+   |     required by a bound introduced by this call
+   |
+   = note: the trait bound `Device: MetaSized` is not satisfied
+note: required by a bound in `Box::<T>::from_raw`
+  --> $SRC_DIR/alloc/src/boxed.rs:LL:COL
+help: consider borrowing here
+   |
+LL |     Box::from_raw(&0 as *mut _)
+   |                   +
+LL |     Box::from_raw(&mut 0 as *mut _)
+   |                   ++++
+
+error[E0277]: the size for values of type `Device` cannot be known
+  --> $DIR/extern-types-unsizing-79409.rs:13:5
+   |
+LL |     Box::from_raw(0 as *mut _)
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a known size
+   |
+   = help: the trait `MetaSized` is not implemented for `Device`
+note: required by a bound in `Box`
+  --> $SRC_DIR/alloc/src/boxed.rs:LL:COL
+
+error[E0277]: the size for values of type `Device` cannot be known
+  --> $DIR/extern-types-unsizing-79409.rs:19:31
+   |
+LL |     let d: Device = unsafe { *make_device() };
+   |                               ^^^^^^^^^^^^^ doesn't have a known size
+   |
+   = help: the trait `MetaSized` is not implemented for `Device`
+note: required by a bound in `Box`
+  --> $SRC_DIR/alloc/src/boxed.rs:LL:COL
+
+error: aborting due to 4 previous errors; 1 warning emitted
+
+For more information about this error, try `rustc --explain E0277`.