[CSSPGO] Enable stale profile matching by default for CSSPGO

We tested the stale profile matching on several Meta's internal services, all results are positive, for instance, in one service that refreshed its profile every one or two weeks, it consistently gave 1~2% performance improvement. We also observed an instance that a trivial refactoring caused a 2% regression and the matching can successfully recover the whole regression. Therefore, we'd like to turn it on by default for CSSPGO.

Reviewed By: hoy, wenlei

Differential Revision: https://reviews.llvm.org/D154027