Rollup merge of rust-lang#97675 - nvzqz:unsized-needs-drop, r=dtolnay

Make `std::mem::needs_drop` accept `?Sized`

This change attempts to make `needs_drop` work with types like `[u8]` and `str`.

This enables code in types like `Arc<T>` that was not possible before, such as rust-lang#97676.

Author: JohnTitor

example/mini_core.rs

@@ -567,7 +567,7 @@ pub mod intrinsics {
         pub fn copy<T>(src: *const T, dst: *mut T, count: usize);
         pub fn transmute<T, U>(e: T) -> U;
         pub fn ctlz_nonzero<T>(x: T) -> T;
-        pub fn needs_drop<T>() -> bool;
+        pub fn needs_drop<T: ?::Sized>() -> bool;
         pub fn bitreverse<T>(x: T) -> T;
         pub fn bswap<T>(x: T) -> T;
         pub fn write_bytes<T>(dst: *mut T, val: u8, count: usize);

example/mini_core_hello_world.rs

@@ -55,6 +55,11 @@ struct NoisyDrop {
     inner: NoisyDropInner,
 }
 
+struct NoisyDropUnsized {
+    inner: NoisyDropInner,
+    text: str,
+}
+
 struct NoisyDropInner;
 
 impl Drop for NoisyDrop {
@@ -170,7 +175,9 @@ fn main() {
         assert_eq!(intrinsics::min_align_of_val(&a) as u8, intrinsics::min_align_of::<&str>() as u8);
 
         assert!(!intrinsics::needs_drop::<u8>());
+        assert!(!intrinsics::needs_drop::<[u8]>());
         assert!(intrinsics::needs_drop::<NoisyDrop>());
+        assert!(intrinsics::needs_drop::<NoisyDropUnsized>());
 
         Unique {
             pointer: NonNull(1 as *mut &str),