do not default on ninja on windows

build.ps1

@@ -3,14 +3,12 @@
 $number_of_build_workers = 8
 $enable_cuda = $true
 $use_vcpkg = $true
-$use_ninja = $true
+$use_ninja = $false
 $force_cpp_build = $false
 
 #$additional_build_setup = " -DCMAKE_CUDA_ARCHITECTURES=30"
 
-
 $CMAKE_EXE = Get-Command cmake | Select-Object -ExpandProperty Definition
-$NINJA_EXE = Get-Command ninja | Select-Object -ExpandProperty Definition
 
 if (-Not $CMAKE_EXE) {
   throw "Could not find CMake, please install it"
@@ -19,11 +17,14 @@ else {
   Write-Host "Using CMake from ${CMAKE_EXE}"
 }
 
-if (-Not $NINJA_EXE -and $use_ninja) {
-  throw "Could not find Ninja, please install it"
-}
-else {
-  Write-Host "Using Ninja from ${NINJA_EXE}"
+if ($use_ninja) {
+  $NINJA_EXE = Get-Command ninja | Select-Object -ExpandProperty Definition
+  if (-Not $NINJA_EXE) {
+    throw "Could not find Ninja, please install it"
+  }
+  else {
+    Write-Host "Using Ninja from ${NINJA_EXE}"
+  }
 }
 
 function getProgramFiles32bit() {