build: Update for newer autoconf.
* configure.ac (AC_PREREQ): Use >= 2.69. (AC_CONFIG_HEADERS): Use it, instead of AC_CONFIG_HEADER. (AC_HEADER_STDC, AC_HEADER_TIME): Remove obsolete macros. (sys/time.h): Add the check of the header. (time_t): Don't use TIME_WITH_SYS_TIME. * acinclude.m4 (AC_HEADER_TIME): Don't require. Don't use TIME_WITH_SYS_TIME. * dirmngr/dns.c: Don't use TIME_WITH_SYS_TIME.
(cherry picked from commit 6b4441a7de9d7090bb3b1570a12e1e8bce0554cb)
- Signed-off-by: NIIBE Yutaka <gniibe@fsij.org>