autoconf 2.56: <resolv.h> detection

[Dimitri PAPADOPOULOS-ORFANOS]

Hi,

There's a problem with <resolv.h> detection on Solaris and
most probably on other UNIX systems.

I can reproduce the bug with autoconf 2.54 and autoconf 2.56.
It hit me while trying to build libxml2 on Solaris:

[...]
configure: WARNING: resolv.h: present but cannot be compiled
configure: WARNING: resolv.h: check for missing prerequisite headers?
configure: WARNING: resolv.h: proceeding with the preprocessor's result
configure: WARNING:     ## ------------------------------------ ##
configure: WARNING:     ## Report this to address@hidden ##
configure: WARNING:     ## ------------------------------------ ##
[...]

See also:
http://bugzilla.gnome.org/show_bug.cgi?id=98880

And indeed configure.in contains:
AC_CHECK_HEADERS(stdlib.h sys/socket.h netinet/in.h arpa/inet.h)
AC_CHECK_HEADERS(sys/timeb.h signal.h arpa/nameser.h resolv.h)

This used to work with autoconf 2.13 but doesn't work with
autoconf 2.54 and better. The problem is that the above
macros expand to a test for <resolv.h> that does not include
<netinet/in.h> and <arpa/nameser.h>. However most UNIX systems
need both <netinet/in.h> and <arpa/nameser.h> to be included
before <resolv.h>. See for example:
http://www.sas.com/service/library/onlinedoc/sasc/doc700/html/lr2/zr2bsdhf.htm
        <resolv.h>
        This header file contains global definitions for the
        resolver. [...] You must include the <sys/types.h>,
        <netinet/in.h>, and <arpa/nameser.h> header files
        before this header file.

Best Regards,
--
Dimitri