Fix lazy ts backend build flags (#75237)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/75237
applies 'OVRSOURCE' logic to one more place missed in D35331263 (https://github.com/pytorch/pytorch/commit/8b7e2bf7a656ef7de12d1c801c8adc9b570cf30f) so that lazy TS backend is not compiled in internal builds
Test Plan: CI
Reviewed By: malfet, shunting314
Differential Revision: D35377758
fbshipit-source-id: 5dcd3d36e50a8917470a917f2120353972dc31ba
(cherry picked from commit 8b8ed7bdaa553eec2ef8b5461d1bd867979049dd)
