Is it normal to get alot of warnings when compling under windows?

I’m following the directions from here:
(I’m building v5.12.0-RC2)

When i get to the ninja step, I get alot of these warnings:

[185/22066] Building CXX object 
C:\pv\pv\VTK\Common\Core\vtkCompositeImplicitBackend.h(80): warning C4251: 'vtkCompositeImplicitBackend<ValueType>::Internal': class 'std::unique_ptr<vtkCompositeImplicitBackend<ValueType>::Internals,std::default_delete<vtkCompositeImplicitBackend<ValueType>::Internals>>' needs to have dll-interface to be used by clients of class 'vtkCompositeImplicitBackend<ValueType>'

Is that normal?

Should I expect the ninja build process to go through without any warnings?

C4251 is a useless warning for projects with more than a single DLL that communicate over a C++ API (in particular, it is saying that you cannot inherit from a class that is not in your own DLL). Just ignore it with -wd4251.