geoip_maxmind: use our own mmdb implementation

This is mainly due to licensing. The libmaxminddb library uses the
Apache license, which meant if we would compile it in by default it
would effectively transform our "GPLv2 or later" to "GPLv3 or later".
Our implementation is ISC licensed, so we can include and enable it
by default and keep things at "GPLv2 or later". This is also why we
used geoip_classic in the first place as default and compiled in,
and not the mmdb variant.

The mmdb.c is based on the specification, using the Go implementation
as a reference during development (ISC licensed), initially implemented
with the help of Claude Opus 4.6. After that substantial changes were
made to make it match UnrealIRCd's style and to make things less error
prone: C style changes, allocation and zero termination of strings in
the library, auto-NULL in variadic functions so the caller cannot
forget NULL there (similar to our unreal_log/do_unreal_log), using
enums as the return type instead of int (similar to curl), adding
doxygen docs, etc.

This also means the old mmdb library dependency has been dropped,
including from configure/autoconf.

At the moment we still use the geoip classic library by default,
including those DB files. The idea is we will switch over sometime
later after this current new MMDB stuff has received more testing.

This also makes us more flexible, since .mmdb files have become the
de-facto standard for pretty much all geoip vendors.

configure

@@ -646,9 +646,6 @@ ac_subst_vars='LTLIBOBJS
 LIBOBJS
 UNRLINCDIR
 IRCDLIBS
-GEOIP_MAXMIND_OBJECTS
-LIBMAXMINDDB_LIBS
-LIBMAXMINDDB_CFLAGS
 GEOIP_CLASSIC_OBJECTS
 GEOIP_CLASSIC_LIBS
 GEOIP_CLASSIC_CFLAGS
@@ -787,7 +784,6 @@ enable_werror
 enable_asan
 enable_libcurl
 enable_geoip_classic
-enable_libmaxminddb
 '
       ac_precious_vars='build_alias
 host_alias
@@ -812,9 +808,7 @@ CARES_LIBS
 JANSSON_CFLAGS
 JANSSON_LIBS
 GEOIP_CLASSIC_CFLAGS
-GEOIP_CLASSIC_LIBS
-LIBMAXMINDDB_CFLAGS
-LIBMAXMINDDB_LIBS'
+GEOIP_CLASSIC_LIBS'
 
 
 # Initialize some variables set by options.
@@ -1452,8 +1446,6 @@ Optional Features:
   --enable-libcurl=DIR    enable libcurl (remote include) support
   --enable-geoip-classic=no/yes
                           enable GeoIP Classic support
-  --enable-libmaxminddb=no/yes
-                          enable GeoIP libmaxminddb support
 
 Optional Packages:
   --with-PACKAGE[=ARG]    use PACKAGE [ARG=yes]
@@ -1534,10 +1526,6 @@ Some influential environment variables:
               C compiler flags for GEOIP_CLASSIC, overriding pkg-config
   GEOIP_CLASSIC_LIBS
               linker flags for GEOIP_CLASSIC, overriding pkg-config
-  LIBMAXMINDDB_CFLAGS
-              C compiler flags for LIBMAXMINDDB, overriding pkg-config
-  LIBMAXMINDDB_LIBS
-              linker flags for LIBMAXMINDDB, overriding pkg-config
 
 Use these variables to override the choices made by 'configure' or to help
 it to find libraries and programs with nonstandard names/locations.
@@ -10147,127 +10135,6 @@ fi
 
 fi
 
-
-	# Check whether --enable-libmaxminddb was given.
-if test ${enable_libmaxminddb+y}
-then :
-  enableval=$enable_libmaxminddb; enable_libmaxminddb=$enableval
-else case e in #(
-  e) enable_libmaxminddb=no ;;
-esac
-fi
-
-
-	if test "x$enable_libmaxminddb" = "xyes"
-then :
-
-				has_system_libmaxminddb="no"
-
-pkg_failed=no
-{ printf "%s\n" "$as_me:${as_lineno-$LINENO}: checking for libmaxminddb >= 1.4.3" >&5
-printf %s "checking for libmaxminddb >= 1.4.3... " >&6; }
-
-if test -n "$LIBMAXMINDDB_CFLAGS"; then
-    pkg_cv_LIBMAXMINDDB_CFLAGS="$LIBMAXMINDDB_CFLAGS"
- elif test -n "$PKG_CONFIG"; then
-    if test -n "$PKG_CONFIG" && \
-    { { printf "%s\n" "$as_me:${as_lineno-$LINENO}: \$PKG_CONFIG --exists --print-errors \"libmaxminddb >= 1.4.3\""; } >&5
-  ($PKG_CONFIG --exists --print-errors "libmaxminddb >= 1.4.3") 2>&5
-  ac_status=$?
-  printf "%s\n" "$as_me:${as_lineno-$LINENO}: \$? = $ac_status" >&5
-  test $ac_status = 0; }; then
-  pkg_cv_LIBMAXMINDDB_CFLAGS=`$PKG_CONFIG --cflags "libmaxminddb >= 1.4.3" 2>/dev/null`
-		      test "x$?" != "x0" && pkg_failed=yes
-else
-  pkg_failed=yes
-fi
- else
-    pkg_failed=untried
-fi
-if test -n "$LIBMAXMINDDB_LIBS"; then
-    pkg_cv_LIBMAXMINDDB_LIBS="$LIBMAXMINDDB_LIBS"
- elif test -n "$PKG_CONFIG"; then
-    if test -n "$PKG_CONFIG" && \
-    { { printf "%s\n" "$as_me:${as_lineno-$LINENO}: \$PKG_CONFIG --exists --print-errors \"libmaxminddb >= 1.4.3\""; } >&5
-  ($PKG_CONFIG --exists --print-errors "libmaxminddb >= 1.4.3") 2>&5
-  ac_status=$?
-  printf "%s\n" "$as_me:${as_lineno-$LINENO}: \$? = $ac_status" >&5
-  test $ac_status = 0; }; then
-  pkg_cv_LIBMAXMINDDB_LIBS=`$PKG_CONFIG --libs "libmaxminddb >= 1.4.3" 2>/dev/null`
-		      test "x$?" != "x0" && pkg_failed=yes
-else
-  pkg_failed=yes
-fi
- else
-    pkg_failed=untried
-fi
-
-
-
-if test $pkg_failed = yes; then
-        { printf "%s\n" "$as_me:${as_lineno-$LINENO}: result: no" >&5
-printf "%s\n" "no" >&6; }
-
-if $PKG_CONFIG --atleast-pkgconfig-version 0.20; then
-        _pkg_short_errors_supported=yes
-else
-        _pkg_short_errors_supported=no
-fi
-        if test $_pkg_short_errors_supported = yes; then
-                LIBMAXMINDDB_PKG_ERRORS=`$PKG_CONFIG --short-errors --print-errors --cflags --libs "libmaxminddb >= 1.4.3" 2>&1`
-        else
-                LIBMAXMINDDB_PKG_ERRORS=`$PKG_CONFIG --print-errors --cflags --libs "libmaxminddb >= 1.4.3" 2>&1`
-        fi
-        # Put the nasty error message in config.log where it belongs
-        echo "$LIBMAXMINDDB_PKG_ERRORS" >&5
-
-        as_fn_error $? "Package requirements (libmaxminddb >= 1.4.3) were not met:
-
-$LIBMAXMINDDB_PKG_ERRORS
-
-Consider adjusting the PKG_CONFIG_PATH environment variable if you
-installed software in a non-standard prefix.
-
-Alternatively, you may set the environment variables LIBMAXMINDDB_CFLAGS
-and LIBMAXMINDDB_LIBS to avoid the need to call pkg-config.
-See the pkg-config man page for more details." "$LINENO" 5
-elif test $pkg_failed = untried; then
-        { printf "%s\n" "$as_me:${as_lineno-$LINENO}: result: no" >&5
-printf "%s\n" "no" >&6; }
-        { { printf "%s\n" "$as_me:${as_lineno-$LINENO}: error: in '$ac_pwd':" >&5
-printf "%s\n" "$as_me: error: in '$ac_pwd':" >&2;}
-as_fn_error $? "The pkg-config script could not be found or is too old.  Make sure it
-is in your PATH or set the PKG_CONFIG environment variable to the full
-path to pkg-config.
-
-Alternatively, you may set the environment variables LIBMAXMINDDB_CFLAGS
-and LIBMAXMINDDB_LIBS to avoid the need to call pkg-config.
-See the pkg-config man page for more details.
-
-To get pkg-config, see <http://pkg-config.freedesktop.org/>.
-See 'config.log' for more details" "$LINENO" 5; }
-else
-        LIBMAXMINDDB_CFLAGS=$pkg_cv_LIBMAXMINDDB_CFLAGS
-        LIBMAXMINDDB_LIBS=$pkg_cv_LIBMAXMINDDB_LIBS
-        { printf "%s\n" "$as_me:${as_lineno-$LINENO}: result: yes" >&5
-printf "%s\n" "yes" >&6; }
-        has_system_libmaxminddb=yes
-fi
-		if test "x$has_system_libmaxminddb" = "xyes"
-then :
-
-
-
-
-
-			GEOIP_MAXMIND_OBJECTS="geoip_maxmind.so"
-
-
-fi
-
-fi
-
-
 UNRLINCDIR="`pwd`/include"
 
 { printf "%s\n" "$as_me:${as_lineno-$LINENO}: checking if explicit -std=gnu17 is needed" >&5