Revert "errno-list: fallback to use our errno name table"

This reverts commit c4ffd0a020.

With this change we fully duplicate the functionality in glibc. This patch
was motivated by glibc missing some names, but those are in the process of
being added:
https://sourceware.org/pipermail/libc-alpha/2025-July/169007.html

src/basic/errno-list.c

@@ -10,7 +10,6 @@ static const struct errno_name* lookup_errno(register const char *str,
                                              register GPERF_LEN_TYPE len);
 
 #include "errno-from-name.inc"
-#include "errno-to-name.inc"
 
 int errno_from_name(const char *name) {
         const struct errno_name *sc;
@@ -25,24 +24,26 @@ int errno_from_name(const char *name) {
         return sc->id;
 }
 
+#if HAVE_STRERRORNAME_NP
 const char* errno_to_name(int id) {
         if (id == 0) /* To stay in line with our own impl */
                 return NULL;
 
+        return strerrorname_np(ABS(id));
+}
+#else
+#  include "errno-to-name.inc"
+
+const char* errno_to_name(int id) {
         if (id < 0)
                 id = -id;
 
-#if HAVE_STRERRORNAME_NP
-        const char *n = strerrorname_np(id);
-        if (n)
-                return n;
-#endif
-
         if ((size_t) id >= ELEMENTSOF(errno_names))
                 return NULL;
 
         return errno_names[id];
 }
+#endif
 
 const char* errno_name_full(int id, char buf[static ERRNO_NAME_BUF_LEN]) {
         const char *a = errno_to_name(id);