clang fails on linux-next since commit 8bf705d13039

[Lukas Bulwahn <lukas.bulwahn@gmail.com>]

Hi Dmitry, hi Ingo,

since commit 8bf705d13039 ("locking/atomic/x86: Switch atomic.h to use atomic-instrumented.h")
on linux-next (tested and bisected from tag next-20180316), compiling the 
kernel with clang fails with:

In file included from arch/x86/entry/vdso/vdso32/vclock_gettime.c:33:
In file included from arch/x86/entry/vdso/vdso32/../vclock_gettime.c:15:
In file included from ./arch/x86/include/asm/vgtod.h:6:
In file included from ./include/linux/clocksource.h:13:
In file included from ./include/linux/timex.h:56:
In file included from ./include/uapi/linux/timex.h:56:
In file included from ./include/linux/time.h:6:
In file included from ./include/linux/seqlock.h:36:
In file included from ./include/linux/spinlock.h:51:
In file included from ./include/linux/preempt.h:81:
In file included from ./arch/x86/include/asm/preempt.h:7:
In file included from ./include/linux/thread_info.h:38:
In file included from ./arch/x86/include/asm/thread_info.h:53:
In file included from ./arch/x86/include/asm/cpufeature.h:5:
In file included from ./arch/x86/include/asm/processor.h:21:
In file included from ./arch/x86/include/asm/msr.h:67:
In file included from ./arch/x86/include/asm/atomic.h:279:
./include/asm-generic/atomic-instrumented.h:295:10: error: invalid output size for constraint '=a'
                return arch_cmpxchg((u64 *)ptr, (u64)old, (u64)new);
                       ^
./arch/x86/include/asm/cmpxchg.h:149:2: note: expanded from macro 'arch_cmpxchg'
        __cmpxchg(ptr, old, new, sizeof(*(ptr)))
        ^
./arch/x86/include/asm/cmpxchg.h:134:2: note: expanded from macro '__cmpxchg'
        __raw_cmpxchg((ptr), (old), (new), (size), LOCK_PREFIX)
        ^
./arch/x86/include/asm/cmpxchg.h:95:17: note: expanded from macro '__raw_cmpxchg'
                             : "=a" (__ret), "+m" (*__ptr)              \
                                     ^

(... and some more similar and closely related errors)

Best regards,

Lukas