Update valgrind version build from source (#38754)
Summary:
Why not use valgrind-3.15.0?
Also, build in in parallel (with -j4)
Pull Request resolved: https://github.com/pytorch/pytorch/pull/38754
Differential Revision: D21657357
Pulled By: malfet
fbshipit-source-id: 22b7761a6c9672477e32f16e56f58bdcce02a75c
