[OpenMPOpt] ICV macro definitions

Summary:
This defines some basic information about ICVs in `OMPKinds.def`.
We also emit remarks with initial values for each function (which are default for now)
as a way to test this.

Reviewers: jdoerfert, JonChesterfield, hamax97, jhuber6

Subscribers: yaxunl, hiraditya, guansong, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D82193