[vtk] fix finding glew issue

[PhoebeHui]

Glew find failed when CMake upgrade to 3.15.2, since FindGLEW.cmake changed in CMake 3.15.2, related issue #7519

VTK has CMake/FindGLEW.cmake, but it removed by 616cfb0ef due to VTK debug was build linked against the release glew library, however this issue fixed in VTK, so I think we should add that back instead of adding others function.

I checked that glew debug library correctly linked in vtk now.

[Neumann-A]

The Problem is the new FindGLEW does not define the variables it promises to define. So the error is on CMake here and the fix in this PR only fixes the VTK issue and no other ports or external cmake projects which still requires those variables. As such I made #7967 to fix the real underlying problem which should work for all dependent projects.

[PhoebeHui]

Thanks for the fix!

[PhoebeHui]

@Neumann-A, thanks for fixing the glew issue, I consider CMake/FindGLEW.cmake in vtk still need add back, what do you think?

[Neumann-A]

@PhoebeHui Why do you think it needs to be added back in? I don't see a reason for it. I also checked the current version from here https://github.com/Kitware/VTK/blob/master/CMake/FindGLEW.cmake and cannot see a reason to add it back into vtk. Config+wrapper seems to be superior to whatever VTK tries to accomplish

[PhoebeHui]

I just think the original reason to remove cmake/FindGLEW.cmake doesn't exsit now, and if add that back, if vtk has changes, vcpkg change accordingly.

[Neumann-A]

If you add it back in the debug build will link wrongly against the release version of glew (debug version has an extra d suffix). That is the reason why it was removed and this reason did not disappear.

[PhoebeHui]

@Neumann-A, thanks, your're right, I double checked, it still linked wrong dll, it's my fault to check the build results in another machine which build with previous cmake version, very appreciate for pointing out this!