Let user be able to change MKLDNN "-m" flags back and forth in subsequent builds (#23608)
Summary:
Currently once user has set `USE_NATIVE_ARCH` to OFF, they will never be able to turn it on for MKLDNN again by simply changing `USE_NATIVE_ARCH`. This commit fixes this issue.
Following up 09ba4df031ed51e05724bb490d4d6fc52b3b1ac6
Pull Request resolved: https://github.com/pytorch/pytorch/pull/23608
Differential Revision: D16599600
Pulled By: ezyang
fbshipit-source-id: 88bbec1b1504b5deba63e56f78632937d003a1f6
