[PATCH] x86, kasan: Fix build failure on KASAN=y && KMEMCHECK=y kernels

[Andrey Ryabinin <aryabinin@virtuozzo.com>]

Declaration of memcpy is hidden under #ifndef CONFIG_KMEMCHECK.
In asm/efi.h we under #ifdef CONFIG_KASAN we #undef memcpy
thus following happens:

In file included from arch/x86/kernel/setup.c:96:0:
./arch/x86/include/asm/desc.h: In function ‘native_write_idt_entry’:
./arch/x86/include/asm/desc.h:122:2: error: implicit declaration of function ‘memcpy’ [-Werror=implicit-function-declaration]
  memcpy(&idt[entry], gate, sizeof(*gate));
  ^
  cc1: some warnings being treated as errors
  make[2]: *** [arch/x86/kernel/setup.o] Error 1

We will get rid of that #undef in asm/efi.h eventually.
But in the meanwhile move memcpy() declaration out ifdefs
to fix build.

Reported-by: Borislav Petkov <bp@alien8.de>
Signed-off-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
---
 arch/x86/include/asm/string_64.h | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/arch/x86/include/asm/string_64.h b/arch/x86/include/asm/string_64.h
index e466119..ff8b9a1 100644
--- a/arch/x86/include/asm/string_64.h
+++ b/arch/x86/include/asm/string_64.h
@@ -27,12 +27,11 @@ static __always_inline void *__inline_memcpy(void *to, const void *from, size_t
    function. */
 
 #define __HAVE_ARCH_MEMCPY 1
+extern void *memcpy(void *to, const void *from, size_t len);
 extern void *__memcpy(void *to, const void *from, size_t len);
 
 #ifndef CONFIG_KMEMCHECK
-#if (__GNUC__ == 4 && __GNUC_MINOR__ >= 3) || __GNUC__ > 4
-extern void *memcpy(void *to, const void *from, size_t len);
-#else
+#if (__GNUC__ == 4 && __GNUC_MINOR__ < 3) || __GNUC__ < 4
 #define memcpy(dst, src, len)					\
 ({								\
 	size_t __len = (len);					\
-- 
2.4.9