Revert "Allow --with-bonjour to work with non-macOS implementations of Bonjour."

Upon further review, our Bonjour code doesn't actually work with the
Avahi not-too-compatible compatibility library.  While you can get it
to work on non-macOS platforms if you link to Apple's own mDNSResponder
code, there don't seem to be many people who care about that.  Leaving in
the AC_SEARCH_LIBS call seems more likely to encourage people to build
broken configurations than to do anything very useful.

Hence, remove the AC_SEARCH_LIBS call and put in a warning comment instead.

Discussion: https://postgr.es/m/2D8331C5-D64F-44C1-8717-63EDC6EAF7EB@brightforge.com

configure

@@ -11124,64 +11124,6 @@ else
 fi
 
 
-  { $as_echo "$as_me:${as_lineno-$LINENO}: checking for library containing DNSServiceRefSockFD" >&5
-$as_echo_n "checking for library containing DNSServiceRefSockFD... " >&6; }
-if ${ac_cv_search_DNSServiceRefSockFD+:} false; then :
-  $as_echo_n "(cached) " >&6
-else
-  ac_func_search_save_LIBS=$LIBS
-cat confdefs.h - <<_ACEOF >conftest.$ac_ext
-/* end confdefs.h.  */
-
-/* Override any GCC internal prototype to avoid an error.
-   Use char because int might match the return type of a GCC
-   builtin and then its argument prototype would still apply.  */
-#ifdef __cplusplus
-extern "C"
-#endif
-char DNSServiceRefSockFD ();
-int
-main ()
-{
-return DNSServiceRefSockFD ();
-  ;
-  return 0;
-}
-_ACEOF
-for ac_lib in '' dns_sd; do
-  if test -z "$ac_lib"; then
-    ac_res="none required"
-  else
-    ac_res=-l$ac_lib
-    LIBS="-l$ac_lib  $ac_func_search_save_LIBS"
-  fi
-  if ac_fn_c_try_link "$LINENO"; then :
-  ac_cv_search_DNSServiceRefSockFD=$ac_res
-fi
-rm -f core conftest.err conftest.$ac_objext \
-    conftest$ac_exeext
-  if ${ac_cv_search_DNSServiceRefSockFD+:} false; then :
-  break
-fi
-done
-if ${ac_cv_search_DNSServiceRefSockFD+:} false; then :
-
-else
-  ac_cv_search_DNSServiceRefSockFD=no
-fi
-rm conftest.$ac_ext
-LIBS=$ac_func_search_save_LIBS
-fi
-{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $ac_cv_search_DNSServiceRefSockFD" >&5
-$as_echo "$ac_cv_search_DNSServiceRefSockFD" >&6; }
-ac_res=$ac_cv_search_DNSServiceRefSockFD
-if test "$ac_res" != no; then :
-  test "$ac_res" = "none required" || LIBS="$ac_res $LIBS"
-
-else
-  as_fn_error $? "could not find function 'DNSServiceRefSockFD' required for Bonjour" "$LINENO" 5
-fi
-
 fi
 
 # for contrib/uuid-ossp

configure.in

@@ -1262,8 +1262,12 @@ fi
 
 if test "$with_bonjour" = yes ; then
   AC_CHECK_HEADER(dns_sd.h, [], [AC_MSG_ERROR([header file <dns_sd.h> is required for Bonjour])])
-  AC_SEARCH_LIBS(DNSServiceRefSockFD, dns_sd, [],
-    [AC_MSG_ERROR([could not find function 'DNSServiceRefSockFD' required for Bonjour])])
+dnl At some point we might add something like
+dnl AC_SEARCH_LIBS(DNSServiceRegister, dns_sd)
+dnl but right now, what that would mainly accomplish is to encourage
+dnl people to try to use the avahi implementation, which does not work.
+dnl If you want to use Apple's own Bonjour code on another platform,
+dnl just add -ldns_sd to LIBS manually.
 fi
 
 # for contrib/uuid-ossp