add a search for GeoIP2 libraries in configure

- "--with-geoip" is used to enable the legacy GeoIP library.
- "--with-geoip2" is used to enable the new GeoIP2 library
  (libmaxminddb), and is on by default if the library is found.
- using both "--with-geoip" and "--with-geoip2" at the same time
  is an error.
- an attempt is made to determine the default GeoIP2 database path at
  compile time if pkg-config is able to report the module prefix. if
  this fails, it will be necessary to set the path in named.conf with
  geoip-directory
- Makefiles have been updated, and a stub lib/dns/geoip2.c has been
  added for the eventual GeoIP2 search implementation.

(cherry picked from commit fea6b5bf10)
(cherry picked from commit 6a7e805796)

util/copyrights

@@ -3323,6 +3323,7 @@
 ./lib/dns/gen-win32.h				C	1999,2000,2001,2004,2005,2006,2007,2009,2014,2016,2018,2019
 ./lib/dns/gen.c					C	1998,1999,2000,2001,2002,2003,2004,2005,2006,2007,2008,2009,2012,2013,2014,2015,2016,2017,2018,2019
 ./lib/dns/geoip.c				C	2013,2014,2015,2016,2018,2019
+./lib/dns/geoip2.c				C	2019
 ./lib/dns/gssapi_link.c				C	2000,2001,2002,2004,2005,2006,2007,2008,2009,2011,2012,2013,2014,2015,2016,2018,2019
 ./lib/dns/gssapictx.c				C	2000,2001,2004,2005,2006,2007,2008,2009,2010,2011,2012,2013,2014,2015,2016,2017,2018,2019
 ./lib/dns/hmac_link.c				C.NAI	1999,2000,2001,2002,2004,2005,2006,2007,2008,2009,2010,2011,2012,2013,2014,2015,2016,2017,2018,2019
@@ -4456,6 +4457,8 @@
 ./libtool.m4/ltversion.m4			X	2012,2018,2019
 ./libtool.m4/lt~obsolete.m4			X	2012,2018,2019
 ./ltmain.sh					X	1999,2000,2001,2003,2004,2006,2009,2012,2018,2019
+./m4/ax_restore_flags.m4			X	2019
+./m4/ax_save_flags.m4				X	2019
 ./make/Makefile.in				MAKE	1998,1999,2000,2001,2004,2007,2012,2016,2018,2019
 ./make/includes.in				MAKE	1999,2000,2001,2004,2005,2007,2012,2014,2016,2018,2019
 ./make/mkdep.in					X	1999,2000,2001,2006,2011,2014,2018,2019