Fixed some build issues with arch

cmake/dependencies/Boost_Sunshine.cmake

@@ -9,9 +9,8 @@ set(BOOST_COMPONENTS
         locale
         log
         program_options
-        system
 )
-# system is not used by Sunshine, but by Simple-Web-Server, added here for convenience
+# boost_system is header-only since Boost 1.69 and has no compiled library since 1.89+
 
 # algorithm, preprocessor, scope, and uuid are not used by Sunshine, but by libdisplaydevice, added here for convenience
 if(WIN32)
@@ -101,3 +100,12 @@ endif()
 
 message(STATUS "Boost include dirs: ${Boost_INCLUDE_DIRS}")
 message(STATUS "Boost libraries: ${Boost_LIBRARIES}")
+
+# boost_system is header-only since Boost 1.69 and has no compiled library in 1.89+.
+# Create a stub INTERFACE target for backward compatibility (e.g., Simple-Web-Server).
+if(NOT TARGET Boost::system)
+    add_library(Boost::system IMPORTED INTERFACE GLOBAL)
+    if(TARGET Boost::headers)
+        target_link_libraries(Boost::system INTERFACE Boost::headers)
+    endif()
+endif()