enable increment build for build_libtorch (#63074)
Summary:
Since issue https://github.com/pytorch/pytorch/issues/59859 is resolved.
rerun_cmake in build_libtorch should not be hardcoded.
build_libtorch is necessary to generate debug version libtorch.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/63074
Reviewed By: VitalyFedyunin, seemethere
Differential Revision: D30306705
Pulled By: malfet
fbshipit-source-id: f2077d334191f4973da0681560937bc8bab730c1
