Fix tyvar_behind_raw_pointer warning

See rust-lang/rust#46906

Author: t-botz

src/rustup-utils/src/raw.rs

@@ -219,7 +219,7 @@ fn symlink_junction_inner(target: &Path, junction: &Path) -> io::Result<()> {
         let mut data = [0u8; MAXIMUM_REPARSE_DATA_BUFFER_SIZE];
         let db = data.as_mut_ptr()
                         as *mut REPARSE_MOUNTPOINT_DATA_BUFFER;
-        let buf = &mut (*db).ReparseTarget as *mut _;
+        let buf = &mut (*db).ReparseTarget as *mut WCHAR;
         let mut i = 0;
         // FIXME: this conversion is very hacky
         let v = br"\??\";