[COMMITTED 2.38] S390: Fix building with --disable-mutli-arch [BZ #31196]

[Stefan Liebler <stli@linux.ibm.com>]

Starting with commits
- 7ea510127e2067efa07865158ac92c330c379950
string: Add libc_hidden_proto for strchrnul
- 22999b2f0fb62eed1af4095d062bd1272d6afeb1
string: Add libc_hidden_proto for memrchr

building glibc on s390x with --disable-multi-arch fails if only
the C-variant of strchrnul / memrchr is used.  This is the case
if gcc uses -march < z13.

The build fails with:
../sysdeps/s390/strchrnul-c.c:28:49: error: ‘__strchrnul_c’ undeclared here (not in a function); did you mean ‘__strchrnul’?
   28 | __hidden_ver1 (__strchrnul_c, __GI___strchrnul, __strchrnul_c);

With --disable-multi-arch, __strchrnul_c is not available as string/strchrnul.c
is just included without defining STRCHRNUL and thus we also don't have to create
the internal hidden symbol.

Tested-by: Andreas K. Hüttel <dilfridge@gentoo.org>
(cherry picked from commit cc1b91eabd806057aa7e3058a84bf129ed36e157)
---
 sysdeps/s390/memrchr-c.c   | 4 +++-
 sysdeps/s390/strchrnul-c.c | 4 +++-
 2 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/sysdeps/s390/memrchr-c.c b/sysdeps/s390/memrchr-c.c
index bdf3c7bbe0..fadd63087a 100644
--- a/sysdeps/s390/memrchr-c.c
+++ b/sysdeps/s390/memrchr-c.c
@@ -25,7 +25,9 @@
 
 # include <string/memrchr.c>
 
-# if defined SHARED && IS_IN (libc)
+# if HAVE_MEMRCHR_IFUNC
+#  if defined SHARED && IS_IN (libc)
 __hidden_ver1 (__memrchr_c, __GI___memrchr, __memrchr_c);
+#  endif
 # endif
 #endif
diff --git a/sysdeps/s390/strchrnul-c.c b/sysdeps/s390/strchrnul-c.c
index f6f5bae311..97fbc16edb 100644
--- a/sysdeps/s390/strchrnul-c.c
+++ b/sysdeps/s390/strchrnul-c.c
@@ -24,7 +24,9 @@
 # endif
 
 # include <string/strchrnul.c>
-# if defined SHARED && IS_IN (libc)
+# if HAVE_STRCHRNUL_IFUNC
+#  if defined SHARED && IS_IN (libc)
 __hidden_ver1 (__strchrnul_c, __GI___strchrnul, __strchrnul_c);
+#  endif
 # endif
 #endif
-- 
2.43.0