Add Linux game server fallback packaging

Scripts/BuildLinuxDedicatedServer-Windows.bat

@@ -10,10 +10,17 @@ set "ARCHIVE_DIR=%PROJECT_DIR%\Builds\LinuxServerDevelopment"
 set "LOG_DIR=%PROJECT_DIR%\Saved\BuildLogs"
 set "LOG_FILE=%LOG_DIR%\BuildLinuxDedicatedServer.log"
 set "TARGET_MAP=/Game/Agrarian/Maps/L_GroundZeroTerrain_Test"
+set "DEFAULT_LINUX_MULTIARCH_ROOT=C:\UnrealToolchains\v26_clang-20.1.8-rockylinux8"
 
 if not exist "%LOG_DIR%" mkdir "%LOG_DIR%"
 if not exist "%ARCHIVE_DIR%" mkdir "%ARCHIVE_DIR%"
 
+if "%LINUX_MULTIARCH_ROOT%"=="" (
+  if exist "%DEFAULT_LINUX_MULTIARCH_ROOT%\x86_64-unknown-linux-gnu\bin\clang++.exe" (
+    set "LINUX_MULTIARCH_ROOT=%DEFAULT_LINUX_MULTIARCH_ROOT%"
+  )
+)
+
 if not exist "%BUILD_BAT%" (
   echo Unreal Engine 5.7 Build.bat was not found at:
   echo %BUILD_BAT%
@@ -37,6 +44,7 @@ echo Archive: %ARCHIVE_DIR%
 echo Log: %LOG_FILE%
 echo.
 echo This requires Epic's Linux cross-compile toolchain for Unreal 5.7 on Windows-Builder.
+echo LINUX_MULTIARCH_ROOT=%LINUX_MULTIARCH_ROOT%
 echo.
 
 call "%BUILD_BAT%" AgrarianGameServer Linux Development -Project="%PROJECT_FILE%" -WaitMutex -NoUBA > "%LOG_FILE%" 2>&1