lib: fix some unnecessary_cast clippy lint

warning: casting raw pointers to the same type and constness is unnecessary (`*mut V` -> `*mut V`)
   --> library\alloc\src\collections\btree\map\entry.rs:357:31
    |
357 |                 let val_ptr = root.borrow_mut().push(self.key, value) as *mut V;
    |                               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `root.borrow_mut().push
(self.key, value)`
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#unnecessary_cast

warning: casting to the same type is unnecessary (`usize` -> `usize`)
   --> library\alloc\src\ffi\c_str.rs:411:56
    |
411 |             let slice = slice::from_raw_parts_mut(ptr, len as usize);
    |                                                        ^^^^^^^^^^^^ help: try: `len`
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#unnecessary_cast

warning: casting raw pointers to the same type and constness is unnecessary (`*mut T` -> `*mut T`)
   --> library\alloc\src\slice.rs:516:25
    |
516 |                         (buf.as_mut_ptr() as *mut T).add(buf.len()),
    |                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `buf.as_mut_ptr()`
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#unnecessary_cast

warning: casting raw pointers to the same type and constness is unnecessary (`*mut T` -> `*mut T`)
   --> library\alloc\src\slice.rs:537:21
    |
537 |                     (buf.as_mut_ptr() as *mut T).add(buf.len()),
    |                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `buf.as_mut_ptr()`
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#unnecessary_cast

warning: casting raw pointers to the same type and constness is unnecessary (`*const ()` -> `*const ()`)
   --> library\alloc\src\task.rs:151:13
    |
151 |             waker as *const (),
    |             ^^^^^^^^^^^^^^^^^^ help: try: `waker`
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#unnecessary_cast

warning: casting raw pointers to the same type and constness is unnecessary (`*const ()` -> `*const ()`)
   --> library\alloc\src\task.rs:323:13
    |
323 |             waker as *const (),
    |             ^^^^^^^^^^^^^^^^^^ help: try: `waker`
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#unnecessary_cast

warning: casting to the same type is unnecessary (`usize` -> `usize`)
   --> library\std\src\sys_common\net.rs:110:21
    |
110 |             assert!(len as usize >= mem::size_of::<c::sockaddr_in>());
    |                     ^^^^^^^^^^^^ help: try: `len`
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#unnecessary_cast

warning: casting to the same type is unnecessary (`usize` -> `usize`)
   --> library\std\src\sys_common\net.rs:116:21
    |
116 |             assert!(len as usize >= mem::size_of::<c::sockaddr_in6>());
    |                     ^^^^^^^^^^^^ help: try: `len`
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#unnecessary_cast

library/alloc/src/collections/btree/map/entry.rs

@@ -354,7 +354,7 @@ impl<'a, K: Ord, V, A: Allocator + Clone> VacantEntry<'a, K, V, A> {
                 // SAFETY: There is no tree yet so no reference to it exists.
                 let map = unsafe { self.dormant_map.awaken() };
                 let mut root = NodeRef::new_leaf(self.alloc.clone());
-                let val_ptr = root.borrow_mut().push(self.key, value) as *mut V;
+                let val_ptr = root.borrow_mut().push(self.key, value);
                 map.root = Some(root.forget_type());
                 map.length = 1;
                 val_ptr

library/alloc/src/ffi/c_str.rs

@@ -408,7 +408,7 @@ impl CString {
                 fn strlen(s: *const c_char) -> usize;
             }
             let len = strlen(ptr) + 1; // Including the NUL byte
-            let slice = slice::from_raw_parts_mut(ptr, len as usize);
+            let slice = slice::from_raw_parts_mut(ptr, len);
             CString { inner: Box::from_raw(slice as *mut [c_char] as *mut [u8]) }
         }
     }

library/alloc/src/slice.rs

@@ -511,9 +511,9 @@ impl<T> [T] {
             while m > 0 {
                 // `buf.extend(buf)`:
                 unsafe {
-                    ptr::copy_nonoverlapping(
+                    ptr::copy_nonoverlapping::<T>(
                         buf.as_ptr(),
-                        (buf.as_mut_ptr() as *mut T).add(buf.len()),
+                        (buf.as_mut_ptr()).add(buf.len()),
                         buf.len(),
                     );
                     // `buf` has capacity of `self.len() * n`.
@@ -532,9 +532,9 @@ impl<T> [T] {
             // `buf.extend(buf[0 .. rem_len])`:
             unsafe {
                 // This is non-overlapping since `2^expn > rem`.
-                ptr::copy_nonoverlapping(
+                ptr::copy_nonoverlapping::<T>(
                     buf.as_ptr(),
-                    (buf.as_mut_ptr() as *mut T).add(buf.len()),
+                    (buf.as_mut_ptr()).add(buf.len()),
                     rem_len,
                 );
                 // `buf.len() + rem_len` equals to `buf.capacity()` (`= self.len() * n`).

library/alloc/src/task.rs

@@ -148,7 +148,7 @@ fn raw_waker<W: Wake + Send + Sync + 'static>(waker: Arc<W>) -> RawWaker {
     unsafe fn clone_waker<W: Wake + Send + Sync + 'static>(waker: *const ()) -> RawWaker {
         unsafe { Arc::increment_strong_count(waker as *const W) };
         RawWaker::new(
-            waker as *const (),
+            waker,
             &RawWakerVTable::new(clone_waker::<W>, wake::<W>, wake_by_ref::<W>, drop_waker::<W>),
         )
     }
@@ -320,7 +320,7 @@ fn local_raw_waker<W: LocalWake + 'static>(waker: Rc<W>) -> RawWaker {
     unsafe fn clone_waker<W: LocalWake + 'static>(waker: *const ()) -> RawWaker {
         unsafe { Rc::increment_strong_count(waker as *const W) };
         RawWaker::new(
-            waker as *const (),
+            waker,
             &RawWakerVTable::new(clone_waker::<W>, wake::<W>, wake_by_ref::<W>, drop_waker::<W>),
         )
     }

library/std/src/sys_common/net.rs

@@ -107,13 +107,13 @@ where
 pub fn sockaddr_to_addr(storage: &c::sockaddr_storage, len: usize) -> io::Result<SocketAddr> {
     match storage.ss_family as c_int {
         c::AF_INET => {
-            assert!(len as usize >= mem::size_of::<c::sockaddr_in>());
+            assert!(len >= mem::size_of::<c::sockaddr_in>());
             Ok(SocketAddr::V4(FromInner::from_inner(unsafe {
                 *(storage as *const _ as *const c::sockaddr_in)
             })))
         }
         c::AF_INET6 => {
-            assert!(len as usize >= mem::size_of::<c::sockaddr_in6>());
+            assert!(len >= mem::size_of::<c::sockaddr_in6>());
             Ok(SocketAddr::V6(FromInner::from_inner(unsafe {
                 *(storage as *const _ as *const c::sockaddr_in6)
             })))