Respect user-set CMAKE_PREFIX_PATH (#61904)
Summary:
Fixes the case where the `CMAKE_PREFIX_PATH` variable gets silently overwritten by a user specified environment variable.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/61904
Reviewed By: walterddr, malfet
Differential Revision: D29792014
Pulled By: cbalioglu
fbshipit-source-id: babacc8d5a1490bff1e14247850cc00c6ba9e6be
