[PATCH] uapi: fix userspace breakage, use __BITS_PER_LONG for swap

[Christian Borntraeger <borntraeger@de.ibm.com>]

QEMU has a funny new build error message when I use the upstream kernel headers:

  CC      block/file-posix.o
In file included from /home/cborntra/REPOS/qemu/include/qemu/timer.h:4,
                 from /home/cborntra/REPOS/qemu/include/qemu/timed-average.h:29,
                 from /home/cborntra/REPOS/qemu/include/block/accounting.h:28,
                 from /home/cborntra/REPOS/qemu/include/block/block_int.h:27,
                 from /home/cborntra/REPOS/qemu/block/file-posix.c:30:
/usr/include/linux/swab.h: In function ‘__swab’:
/home/cborntra/REPOS/qemu/include/qemu/bitops.h:20:34: error: "sizeof" is not defined, evaluates to 0 [-Werror=undef]
   20 | #define BITS_PER_LONG           (sizeof (unsigned long) * BITS_PER_BYTE)
      |                                  ^~~~~~
/home/cborntra/REPOS/qemu/include/qemu/bitops.h:20:41: error: missing binary operator before token "("
   20 | #define BITS_PER_LONG           (sizeof (unsigned long) * BITS_PER_BYTE)
      |                                         ^
cc1: all warnings being treated as errors
make: *** [/home/cborntra/REPOS/qemu/rules.mak:69: block/file-posix.o] Error 1
rm tests/qemu-iotests/socket_scm_helper.o

This was triggered by commit d5767057c9a ("uapi: rename ext2_swab() to swab() and share globally in swab.h")
This patch is doing
+#include <asm/bitsperlong.h>
but it uses BITS_PER_LONG.

The kernel file asm/bitsperlong.h provide only __BITS_PER_LONG.

Let us use the __ variant in swap.h
Fixes: d5767057c9a ("uapi: rename ext2_swab() to swab() and share globally in swab.h")
Cc: Yury Norov <yury.norov@gmail.com>
Cc: Allison Randal <allison@lohutok.net>
Cc: Joe Perches <joe@perches.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: William Breathitt Gray <vilhelm.gray@gmail.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
---
 include/uapi/linux/swab.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/include/uapi/linux/swab.h b/include/uapi/linux/swab.h
index fa7f97da5b76..7272f85d6d6a 100644
--- a/include/uapi/linux/swab.h
+++ b/include/uapi/linux/swab.h
@@ -135,9 +135,9 @@ static inline __attribute_const__ __u32 __fswahb32(__u32 val)
 
 static __always_inline unsigned long __swab(const unsigned long y)
 {
-#if BITS_PER_LONG == 64
+#if __BITS_PER_LONG == 64
 	return __swab64(y);
-#else /* BITS_PER_LONG == 32 */
+#else /* __BITS_PER_LONG == 32 */
 	return __swab32(y);
 #endif
 }
-- 
2.24.1