Attempt to fix Windows test failure caused by r338133

It seems like the pass pipeline on Windows is slightly different than on Linux
and macOS. As a result, the arm64-opt-remarks-lazy-bfi test has been failing.

This switches a CHECK-NEXT to a CHECK-DAG to try and get this running properly
again.

It'd be nice to switch it back to a CHECK-NEXT if possible, but the CHECK-NEXT
lines following the line we care about (the optimization remark emitter)
do a pretty good job of enforcing the ordering we want.

Hopefully this works, since I don't have a Windows machine. ;)

Example failure: http://lab.llvm.org:8011/builders/llvm-clang-x86_64-expensive-checks-win/builds/11295

llvm-svn: 338267