c++ - How to set cmake option with ninja without calling vcvarsall.bat to compile x86 and x64 each of parent and child project?

Question

I want to build project with Ninja in Visual Studio 2019 environment. To do this, I have to call vcvarsall.bat. I want to build parent project with x64 while build subproject with x86. When I call vcvars64.bat, I cannot compile subproject with x86. So I am going to set compiler with x64 and x86 env each of parent project and subproject. How to set this option in CMakeLists.txt file?