include/linux/bitops.h: avoid clang shift-count-overflow warnings

Clang normally does not warn about certain issues in inline functions when
it only happens in an eliminated code path. However if something else
goes wrong, it does tend to complain about the definition of hweight_long()
on 32-bit targets:

  include/linux/bitops.h:75:41: error: shift count >= width of type [-Werror,-Wshift-count-overflow]
          return sizeof(w) == 4 ? hweight32(w) : hweight64(w);
                                                 ^~~~~~~~~~~~
  include/asm-generic/bitops/const_hweight.h:29:49: note: expanded from macro 'hweight64'
   define hweight64(w) (__builtin_constant_p(w) ? __const_hweight64(w) : __arch_hweight64(w))
                                                  ^~~~~~~~~~~~~~~~~~~~
  include/asm-generic/bitops/const_hweight.h:21:76: note: expanded from macro '__const_hweight64'
   define __const_hweight64(w) (__const_hweight32(w) + __const_hweight32((w) >> 32))
                                                                             ^  ~~
  include/asm-generic/bitops/const_hweight.h:20:49: note: expanded from macro '__const_hweight32'
   define __const_hweight32(w) (__const_hweight16(w) + __const_hweight16((w) >> 16))
                                                  ^
  include/asm-generic/bitops/const_hweight.h:19:72: note: expanded from macro '__const_hweight16'
   define __const_hweight16(w) (__const_hweight8(w)  + __const_hweight8((w)  >> 8 ))
                                                                         ^
  include/asm-generic/bitops/const_hweight.h:12:9: note: expanded from macro '__const_hweight8'
            (!!((w) & (1ULL << 2))) +     \

Adding an explicit cast to __u64 avoids that warning and makes it easier
to read other output.
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Christian Brauner <christian.brauner@ubuntu.com>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Nick Desaulniers <ndesaulniers@google.com>
Link: http://lkml.kernel.org/r/20200505135513.65265-1-arnd@arndb.deSigned-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/bitops.h

@@ -72,7 +72,7 @@ static inline int get_bitmask_order(unsigned int count)
 
 static __always_inline unsigned long hweight_long(unsigned long w)
 {
-	return sizeof(w) == 4 ? hweight32(w) : hweight64(w);
+	return sizeof(w) == 4 ? hweight32(w) : hweight64((__u64)w);
 }
 
 /**