Bump required minimum version of glibc to 2.34

Major distributions already have glibc >= 2.34.
Let's bump the required minimum version.

Note, glibc-2.34 was released on 2021-08-01.

src/basic/errno-list.c

@@ -24,7 +24,7 @@ int errno_from_name(const char *name) {
         return sc->id;
 }
 
-#if HAVE_STRERRORNAME_NP
+#ifdef __GLIBC__
 const char* errno_name_no_fallback(int id) {
         if (id == 0) /* To stay in line with our implementation below.  */
                 return NULL;