configure: Make sure the check for newer libplist works as expected

Author: nikias

configure.ac

@@ -94,15 +94,14 @@ AM_CONDITIONAL(WIN32, test x$win32 = xtrue)
 AC_CHECK_MEMBER(struct dirent.d_type, AC_DEFINE(HAVE_DIRENT_D_TYPE, 1, [define if struct dirent has member d_type]),, [#include <dirent.h>])
 
 CACHED_CFLAGS="$CFLAGS"
-CFLAGS+=" $libplist_CFLAGS"
+CFLAGS+=" $libplist_CFLAGS -Werror"
 
 # check if libplist has plist_new_unix_date()
 AC_CACHE_CHECK(for plist_new_unix_date, ac_cv_plist_unix_date,
 	AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[
 		#include <plist/plist.h>
 		]], [[
-			plist_new_unix_date(0);
-                        return 0;
+			return plist_new_unix_date(0) ? 0 : 1
 		]])],[ac_cv_plist_unix_date=yes],[ac_cv_plist_unix_date=no]))
 if test "$ac_cv_plist_unix_date" = "yes"; then
 	AC_DEFINE(HAVE_PLIST_UNIX_DATE, 1, [Define if libplist has new unix date API (>= 2.7.0)])