Add build_variable.bzl to CMAKE_RERUN target (#36809)
Summary:
`configure_file` command adds its input as a top-level dependency triggering make file regeneration if file timestamp have changed
Also abort CMAKE if `exec` of build_variables.bzl failed for some reason
Pull Request resolved: https://github.com/pytorch/pytorch/pull/36809
Test Plan: Add invalid statement to build_variables.bzl and check that build process fails
Differential Revision: D21100721
Pulled By: malfet
fbshipit-source-id: 79a54aa367fb8dedb269c78b9538b4da203d856b
