clippy: fix ptr_cast_constness lint

https://rust-lang.github.io/rust-clippy/master/index.html#ptr_cast_constness

Cargo.toml

@@ -667,7 +667,6 @@ should_panic_without_expect = "allow"        # 2
 doc_markdown = "allow"
 unused_self = "allow"
 enum_glob_use = "allow"
-ptr_cast_constness = "allow"
 needless_raw_string_hashes = "allow"
 unreadable_literal = "allow"
 unnested_or_patterns = "allow"

src/uucore/src/lib/features/entries.rs

@@ -290,7 +290,7 @@ macro_rules! f {
                 unsafe {
                     let data = $fid(k);
                     if !data.is_null() {
-                        Ok($st::from_raw(ptr::read(data as *const _)))
+                        Ok($st::from_raw(ptr::read(data.cast_const())))
                     } else {
                         // FIXME: Resource limits, signals and I/O failure may
                         // cause this too. See getpwnam(3).
@@ -317,12 +317,12 @@ macro_rules! f {
                     // f!(getgrnam, getgrgid, gid_t, Group);
                     let data = $fnam(cstring.as_ptr());
                     if !data.is_null() {
-                        return Ok($st::from_raw(ptr::read(data as *const _)));
+                        return Ok($st::from_raw(ptr::read(data.cast_const())));
                     }
                     if let Ok(id) = k.parse::<$t>() {
                         let data = $fid(id);
                         if !data.is_null() {
-                            Ok($st::from_raw(ptr::read(data as *const _)))
+                            Ok($st::from_raw(ptr::read(data.cast_const())))
                         } else {
                             Err(IOError::new(
                                 ErrorKind::NotFound,

src/uucore/src/lib/features/utmpx.rs

@@ -525,7 +525,7 @@ impl Iterator for UtmpxIter {
                 // All the strings live inline in the struct as arrays, which
                 // makes things easier.
                 Some(UtmpxRecord::Traditional(Box::new(Utmpx {
-                    inner: ptr::read(res as *const _),
+                    inner: ptr::read(res.cast_const()),
                 })))
             }
         }