[cmake] add HAVE_SOVERSION option (default=OFF). (#37502)
Summary:
This is useful for linux distributions when the ABI/API of libtorch has
been changed. The default SOVERSION is set to
"${TORCH_VERSION_MAJOR}.${TORCH_VERSION_MINOR}".
ezyang
But if the release strategy of pytorch/caffe2 involves avoiding breaking API/ABI changes to libtorch for minor/patch releases, then we can set `TORCH_SOVERSION` to simply `TORCH_VERSION_MAJOR`. Please confirm that.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/37502
Differential Revision: D21303565
Pulled By: ezyang
fbshipit-source-id: 798f5ec7fc5f0431ff1a7f9e8e5d3a0d3b25bb22
