set USE_STATIC_DISPATCH outside cmake (#29715)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/29715
Previous we hard code it to enable static dispatch when building mobile
library. Since we are exploring approaches to deprecate static dispatch
we should make it optional. This PR moved the setting from cmake to bash
build scripts which can be overridden.
Test Plan: - verified it's still using static dispatch when building with these scripts.
Differential Revision: D18474640
Pulled By: ljk53
fbshipit-source-id: 7591acc22009bfba36302e3b2a330b1428d8e3f1
