[Coroutines][3/6] New pass manager: coro-elide

Summary:
Depends on https://reviews.llvm.org/D71899.

The third in a series of patches that ports the LLVM coroutines passes
to the new pass manager infrastructure. This patch implements 'coro-elide'.

The new pass manager infrastructure does not implicitly repeat CGSCC
pass pipelines when a function is devirtualized, and so the tests
for the new pass manager that rely on that behavior now explicitly
specify `repeat<2>`.

Reviewers: GorNishanov, lewissbaker, chandlerc, jdoerfert, junparser, deadalnix, wenlei

Reviewed By: wenlei

Subscribers: wenlei, EricWF, Prazek, hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D71900