MDEV-37600 fixup: clang 21 -Wunterminated-string-initialization

Author: dr-m

plugin/auth_mysql_sha2/sha256crypt.c

@@ -32,6 +32,9 @@ void sha256_crypt_r(const unsigned char *key, size_t key_len,
   static const char b64t[64]
 #if defined __GNUC__ && __GNUC__ > 7
     __attribute__((nonstring))
+#endif
+#if defined __clang_major__ && __clang_major__ > 20
+    __attribute__((nonstring))
 #endif
     = "./0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz";
   void *ctx = alloca(my_sha256_context_size());