move module_save.cpp to non-mobile build section in cmake (#30221)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/30221
PR #29881 moved Module::save() methods to a separate source file
and removed C10_MOBILE gating logic. Seems it should stay with
export_module.cpp (which is in "NOT INTERN_BUILD_MOBILE" section).
Otherwise it causes link error with build_mobile.sh.
Test:
- build locally
- check CI
Test Plan: Imported from OSS
Differential Revision: D18649234
Pulled By: ljk53
fbshipit-source-id: b6c90a532d191c41ce10c1047a869d8f73854c4d
