Unify caffe2 and libtorch build scripts on Windows (#18683)
Summary:
`scripts/build_windows.bat` is the original way to build caffe2 on Windows, but since it is merged into libtorch, the build scripts should be unified because they actually do the same thing except there are some different flags.
The follow-up is to add the tests. Looks like the CI job for caffe2 windows is defined [here](https://github.com/pytorch/ossci-job-dsl/blob/master/src/jobs/caffe2.groovy#L906). Could we make them a separate file, just like what we've done in `.jenkins/pytorch/win-build.sh`? There's a bunch of things we can do there, like using ninja and sccache to accelerate build.
cc orionr yf225
Pull Request resolved: https://github.com/pytorch/pytorch/pull/18683
Differential Revision: D14730188
Pulled By: ezyang
fbshipit-source-id: ea287d7f213d66c49faac307250c31f9abeb0ebe
