[SafeStack,NFC] Move SafeStackColoring code

Summary:
This code is going to be used in StackSafety.
This patch is file move with minimal changes. Identifiers
will be fixed in the followup patch.

Reviewers: eugenis, pcc

Reviewed By: eugenis

Subscribers: mgorny, hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D81831