s390/purgatory: do not build purgatory with kcov, kasan and friends

[ Upstream commit c23587c92f6e3260fe3b82bb75b38aa2553b9468 ]

the purgatory must not rely on functions from the "old" kernel,
so we must disable kasan and friends. We also need to have a
separate copy of string.c as the default does not build memcmp
with KASAN.
Reported-by: Nkbuild test robot <lkp@intel.com>
Signed-off-by: NChristian Borntraeger <borntraeger@de.ibm.com>
Reviewed-by: NVasily Gorbik <gor@linux.ibm.com>
Signed-off-by: NVasily Gorbik <gor@linux.ibm.com>
Signed-off-by: NSasha Levin <sashal@kernel.org>
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>

arch/s390/purgatory/Makefile

@@ -13,8 +13,10 @@ $(obj)/sha256.o: $(srctree)/lib/sha256.c FORCE
 $(obj)/mem.o: $(srctree)/arch/s390/lib/mem.S FORCE
 	$(call if_changed_rule,as_o_S)
 
-$(obj)/string.o: $(srctree)/arch/s390/lib/string.c FORCE
-	$(call if_changed_rule,cc_o_c)
+KCOV_INSTRUMENT := n
+GCOV_PROFILE := n
+UBSAN_SANITIZE := n
+KASAN_SANITIZE := n
 
 LDFLAGS_purgatory.ro := -e purgatory_start -r --no-undefined -nostdlib
 LDFLAGS_purgatory.ro += -z nodefaultlib

arch/s390/purgatory/string.c

+// SPDX-License-Identifier: GPL-2.0
+#define __HAVE_ARCH_MEMCMP	/* arch function */
+#include "../lib/string.c"