Converts the BUILD_BUG to a WARN to allow building with a low/unoptimised
compiler.

The original expectation was that a compiler would see that the only
usage of this function was in a function that is only called behind
radix-only guards. And it worked this way on GCC. It seems Clang does
not optimise away this call however, so thinks the function may be
invoked and triggers the build bug as reported by the kernel test robot.

https://lore.kernel.org/llvm/202301212348.eDkowvfF-lkp@intel.com (local)

This fix converts the build bug to a warning to allow builds without
relying on particular compiler optimisation behaviours. The warning is
not rate limited because this implementation should still never be called
as-is, and anyone who might invoke it might appreciate it being very
obvious that it's not behaving as expected.

Fixes: 274d842fa1ef ("powerpc/tlb: Add local flush for page given mm_struct and psize")
Reported-by: kernel test robot <redacted>
Signed-off-by: Benjamin Gray <redacted>
---
 arch/powerpc/include/asm/book3s/32/tlbflush.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/powerpc/include/asm/book3s/32/tlbflush.h b/arch/powerpc/include/asm/book3s/32/tlbflush.h
index 4be572908124..675196884640 100644
--- a/arch/powerpc/include/asm/book3s/32/tlbflush.h
+++ b/arch/powerpc/include/asm/book3s/32/tlbflush.h

@@ -2,7 +2,7 @@
 #ifndef _ASM_POWERPC_BOOK3S_32_TLBFLUSH_H
 #define _ASM_POWERPC_BOOK3S_32_TLBFLUSH_H
 
-#include <linux/build_bug.h>
+#include <linux/bug.h>
 
 #define MMU_NO_CONTEXT      (0)
 /*

@@ -80,7 +80,7 @@ static inline void local_flush_tlb_page(struct vm_area_struct *vma,
 static inline void local_flush_tlb_page_psize(struct mm_struct *mm,
 					      unsigned long vmaddr, int psize)
 {
-	BUILD_BUG();
+	WARN(1, "Unimplemented local TLB flush with psize");