[Loop Peeling] Enable peeling of multiple exits by default.

Enable loop peeling with multiple exits where all non-latch exits
ends up with deopt by default.

Reviewers: reames, fhahn
Reviewed By: reames
Subscribers: xbolva00, hiraditya, zzheng, llvm-commits
Differential Revision: https://reviews.llvm.org/D64619

llvm-svn: 366542