Fix Irrlicht build bug

Enable Irrlicht GUI automatically when IrrlichtDir is set in build.ps1

Author: dav-og

build.ps1

@@ -603,6 +603,7 @@ function Get-BuildArguments {
     $irrlicht   = ($Config.IrrlichtDir -replace '\\','/')
     $irrlichtDllWin = Join-Path $Config.IrrlichtDir "bin\Win64-VisualStudio\Irrlicht.dll"
     $irrlichtDll = ($irrlichtDllWin -replace '\\','/')
+    $irrlichtFlag = if ($Config.IrrlichtDir -and (Test-Path $Config.IrrlichtDir)) { "ON" } else { "OFF" }
 
     # Deterministic prefix path so our roots win over ambient environment
     $prefixParts = @()
@@ -623,6 +624,7 @@ function Get-BuildArguments {
         "-DEIGEN3_INCLUDE_DIR=`"$eigenDir`"",
         "-DIrrlicht_ROOT=`"$irrlicht`"",
         "-DIRRLICHT_DLL_PATH=`"$irrlichtDll`"",
+        "-DHYDROCHRONO_ENABLE_IRRLICHT=`"$irrlichtFlag`"",
         "-DCMAKE_PREFIX_PATH=`"$prefixPath`"",
         "-DCMAKE_FIND_PACKAGE_PREFER_CONFIG=ON",
         "-DCMAKE_FIND_USE_PACKAGE_REGISTRY=OFF",