__lwsync macro breakage with ARCH=powerpc

[nathanchance]

llvm/llvm-project@62b5df7 causes a macro definition collision:

In file included from arch/powerpc/kernel/pmc.c:12:
In file included from include/linux/bug.h:5:
In file included from arch/powerpc/include/asm/bug.h:109:
In file included from include/asm-generic/bug.h:20:
In file included from include/linux/kernel.h:12:
In file included from include/linux/bitops.h:32:
In file included from arch/powerpc/include/asm/bitops.h:62:
arch/powerpc/include/asm/barrier.h:49:9: error: '__lwsync' macro redefined [-Werror,-Wmacro-redefined]
#define __lwsync() __asm__ __volatile__ (stringify_in_c(LWSYNC) : : :"memory")
 ^
<built-in>:308:9: note: previous definition is here
#define __lwsync __builtin_ppc_lwsync
 ^
1 error generated.

Patch submitted: https://lore.kernel.org/r/20210528182752.1852002-1-nathan@kernel.org/

[nathanchance]

Accepted: https://git.kernel.org/powerpc/c/015d98149b32