TARGET_CXX is added, because PowerDNS now uses C++17.

pdns.conf-dist is updated to the latest version shipped by PowerDNS.

010-time_t-check.patch, which is also used in pdns-recursor and dnsdist,
is added to patch out the check for 64-bit time_t,
because OpenWrt still supports 32-bit devices.

100-pdns-disable-pdns.conf-dist.patch is refreshed.

Signed-off-by: Wout Bertrums <wout@wbnet.eu>