Boost.System no longer has a library.

--- mkvtoolnix-94.0/ac/boost.m4	2025-07-27 17:23:09.000000000 +0100
+++ mkvtoolnix-94.0/ac/boost.m4	2025-08-15 04:15:30.401134581 +0100
@@ -36,9 +36,6 @@
 fi
 AC_MSG_RESULT([yes])
 
-# boost::system must be present.
-AX_BOOST_SYSTEM()
-
 # boost::filesystem must be present.
 AX_BOOST_FILESYSTEM()
 
@@ -46,10 +43,6 @@
   AC_MSG_ERROR(The Boost Filesystem Library was not found.)
 fi
 
-if test x"$ax_cv_boost_system" != "xyes"; then
-  AC_MSG_ERROR(The Boost System Library was not found.)
-fi
-
 AX_BOOST_CHECK_HEADERS([boost/operators.hpp],,[
   AC_MSG_ERROR([Boost's Operators library is required but wasn't found])
 ])
--- mkvtoolnix-94.0/rake.d/target.rb	2025-07-27 17:23:09.000000000 +0100
+++ mkvtoolnix-94.0/rake.d/target.rb	2025-08-15 04:22:20.675250340 +0100
@@ -164,7 +164,6 @@
       when :cmark            then c(:CMARK_LIBS)
       when :dvdread          then c(:DVDREAD_LIBS)
       when :boost_filesystem then c(:BOOST_FILESYSTEM_LIB)
-      when :boost_system     then c(:BOOST_SYSTEM_LIB)
       when :pugixml          then c?(:PUGIXML_INTERNAL) ? [ '-Llib/pugixml/src', '-lpugixml' ] : c(:PUGIXML_LIBS)
       when :qt               then c(:QT_LIBS)
       when :qt_non_gui       then c(:QT_LIBS_NON_GUI)
--- mkvtoolnix-94.0/Rakefile	2025-07-27 17:23:09.000000000 +0100
+++ mkvtoolnix-94.0/Rakefile	2025-08-15 06:09:56.179782077 +0100
@@ -1090,7 +1090,6 @@
 # libraries required for all programs via mtxcommon
 $common_libs = [
   :boost_filesystem,
-  :boost_system,
   :flac,
   :z,
   :pugixml,