powerpc: prepare string/mem functions for KASAN

CONFIG_KASAN implements wrappers for memcpy() memmove() and memset()
Those wrappers are doing the verification then call respectively
__memcpy() __memmove() and __memset(). The arches are therefore
expected to rename their optimised functions that way.

For files on which KASAN is inhibited, #defines are used to allow
them to directly call optimised versions of the functions without
going through the KASAN wrappers.

See commit 393f203f5f ("x86_64: kasan: add interceptors for
memset/memmove/memcpy functions") for details.

Other string / mem functions do not (yet) have kasan wrappers,
we therefore have to fallback to the generic versions when
KASAN is active, otherwise KASAN checks will be skipped.

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
[mpe: Fixups to keep selftests working]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

tools/testing/selftests/powerpc/copyloops/asm/export.h

@@ -1,2 +1,3 @@
 /* SPDX-License-Identifier: GPL-2.0 */
 #define EXPORT_SYMBOL(x)
+#define EXPORT_SYMBOL_KASAN(x)

tools/testing/selftests/powerpc/copyloops/asm/ppc_asm.h

@@ -25,6 +25,7 @@
 
 #define _GLOBAL(A) FUNC_START(test_ ## A)
 #define _GLOBAL_TOC(A) _GLOBAL(A)
+#define _GLOBAL_TOC_KASAN(A) _GLOBAL(A)
 
 #define PPC_MTOCRF(A, B)	mtocrf A, B