Print out DebugCounter info with -print-debug-counter

Print out DebugCounter info with -print-debug-counter

Summary:
This patch will print out {Counter, Skip, StopAfter} info of all passes which have DebugCounter set at destruction.

It can be used to monitor how many times does certain transformation happen in a pass, and also help check if -debug-counter option is set correctly.

Please refer to this [[ http://lists.llvm.org/pipermail/llvm-dev/2018-July/124722.html  | thread ]] for motivation.

Reviewers: george.burgess.iv, davide, greened

Reviewed By: greened

Subscribers: kristina, llozano, mgorny, llvm-commits, mgrang

Differential Revision: https://reviews.llvm.org/D50031

llvm-svn: 345085