build: Improve test for ADNS

* configure.ac <adns>: Use adns_free as probe function for libadns.
(HAVE_ADNS_FREE): Remove bogus tests to set this and remove the macro.
(ADNSLIBS): Do not ac_subst - it is only used within configure.
--

adns_free is required on Windows anyway (for robustness reasons) and
it has been around for so long now that we do not need a separate
test.  An upstream adns 1.5 has meanwhile been release but I doubt that
this has the required Windows code - and it is not libtool based
anyway.

common/dns-cert.c

@@ -44,9 +44,6 @@
 #endif
 #ifdef USE_ADNS
 # include <adns.h>
-# ifndef HAVE_ADNS_FREE
-#  define adns_free free
-# endif
 #endif
 
 #include "util.h"

common/pka.c

@@ -48,9 +48,6 @@
 #endif /* USE_DNS_PKA */
 #ifdef USE_ADNS
 # include <adns.h>
-# ifndef HAVE_ADNS_FREE
-#  define adns_free free
-# endif
 #endif
 
 #include "util.h"

common/srv.c

@@ -45,9 +45,6 @@
 #include <time.h>
 #ifdef USE_ADNS
 # include <adns.h>
-# ifndef HAVE_ADNS_FREE
-#  define adns_free free
-# endif
 #endif
 
 #include "util.h"

configure.ac

@@ -904,18 +904,14 @@ AC_ARG_WITH(adns,
              fi])
 if test "$with_adns" != "no"; then
   AC_CHECK_HEADERS(adns.h,
-                AC_CHECK_LIB(adns, adns_init,
+                AC_CHECK_LIB(adns, adns_free,
                              [have_adns=yes],
                              [CPPFLAGS=${_cppflags} LDFLAGS=${_ldflags}]),
-                [CPPFLAGS=${_cppflags} LDFLAGS=${_ldflags}])
+                             [CPPFLAGS=${_cppflags} LDFLAGS=${_ldflags}])
 fi
 if test "$have_adns" = "yes"; then
   ADNSLIBS="-ladns"
 fi
-AC_SUBST(ADNSLIBS)
-# Newer adns versions feature a free function to be used under W32.
-AC_CHECK_FUNCS(adns_free)
-
 
 
 #