* 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.