Re: [PATCH 2/2] compiler.h: Include asm/rwonce.h under ARM64 and ALPHA to fix build errors

When make M=samples/bpf on the Loongson 3A3000 platform which
belongs to MIPS arch, there exists many similar build errors
about 'asm/rwonce.h' file not found, so include it only under
CONFIG_ARM64 and CONFIG_ALPHA due to it exists only in arm64
and alpha arch.

   CLANG-bpf  samples/bpf/xdpsock_kern.o
In file included from samples/bpf/xdpsock_kern.c:2:
In file included from ./include/linux/bpf.h:9:
In file included from ./include/linux/workqueue.h:9:
In file included from ./include/linux/timer.h:5:
In file included from ./include/linux/list.h:9:
In file included from ./include/linux/kernel.h:10:
./include/linux/compiler.h:246:10: fatal error: 'asm/rwonce.h' file not found
          ^~~~~~~~~~~~~~
1 error generated.

$ find . -name rwonce.h
./include/asm-generic/rwonce.h
./arch/arm64/include/asm/rwonce.h
./arch/alpha/include/asm/rwonce.h

Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
---
  include/linux/compiler.h | 6 ++++++
  1 file changed, 6 insertions(+)

diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index b8fe0c2..bdbe759 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h

@@ -243,6 +243,12 @@ static inline void *offset_to_ptr(const int *off)
   */
  #define prevent_tail_call_optimization()	mb()
  
+#ifdef CONFIG_ARM64