We require POSIX.1-2001. Some systems provide it only with feature
test macro _POSIX_C_SOURCE defined to 200112L. Since we don't define
it, the build fails there. Observed on Solaris 10.
We actually require the XSI extension. The GNU C Library provides it
by default. With _POSIX_C_SOURCE 200112L, however, you have to define
feature test macro _XOPEN_SOURCE to get it. But then _POSIX_C_SOURCE
is redundant.
Make configure put #define _XOPEN_SOURCE 600 into config.h. Drop the
two existing #define _XOPEN_SOURCE 500 in .c files.
Now Solaris cc refuses to play ball unless switched to C99. Replace
AC_PROG_CC by AC_PROG_CC_STDC to mollify it.
Unfortunately, use of _XOPEN_SOURCE exposes bugs in AIX libc and old
versions of GNU libc:
* AIX defines struct in6_addr's member s6_addr as a macro expanding
into the actual member. Without _ALL_SOURCE (the default), the
expansion is wrong and doesn't compile. Observed with AIX V7.2.
* GNU lib's IN6_IS_ADDR_V4MAPPED() is unusable without
_DEFAULT_SOURCE (default) or _GNU_SOURCE. Observed with Debian 8.
Tracked at <https://sourceware.org/bugzilla/show_bug.cgi?id=16421>,
fixed in version 2.25.
Affects just sockaddr_ntop()'s special case from commit 372cdb136 "Use
IPv4 format for IPv4-mapped addresses", v4.3.31. Disable the special
case and use IPv6 format on such systems. This is a very minor
usability regression. Could be avoided, I guess, but it's not worth
the trouble.
Signed-off-by: Markus Armbruster <armbru@pond.sub.org>
