next-20220715 build fail due to 579b9239c1f386 (powerpc, ps3_defconfig, GCC 12.1.0)

[Bagas Sanjaya]

Hi everyone,

I built next-20220715 tree, using powerpc64-unknown-linux-gnu-gcc
(GCC 12.1.0) and ps3_defconfig. The build errored on W=1 build
(-Werror=missing-prototypes):

  CC      arch/powerpc/mm/book3s64/pgtable.o
  CC      arch/powerpc/kernel/process.o
arch/powerpc/mm/book3s64/pgtable.c:478:5: error: no previous prototype for 'pmd_move_must_withdraw' [-Werror=missing-prototypes]
  478 | int pmd_move_must_withdraw(struct spinlock *new_pmd_ptl,
      |     ^~~~~~~~~~~~~~~~~~~~~~
cc1: all warnings being treated as errors

The errored line is introduced by commit 579b9239c1f386 ("powerpc/radix: Fix
kernel crash with mremap()")

Looking at the commit, it seems like GCC didn't see the prototype which had
already been given, or am I missing something?

Thanks.

-- 
An old man doll... just what I always wanted! - Clara