Reported by Bruno Haible in
<https://lists.gnu.org/archive/html/bug-gnulib/2024-05/msg00290.html>.
* lib/endian.in.h (be16toh, be32toh, be64toh, htobe16, htobe32, htobe64)
(le16toh, le32toh, le64toh, htole16, htole32, htole64): Don't define
functions if the system has working versions.
* m4/endian_h.m4 (gl_ENDIAN_H): Separate checks for stdint types and
proper macro/function definitions.
* modules/endian (Depends-on): Add include_next. Update module
dependency conditions.
(Makefile.am): Perform sed replacements on the header substitute.