[clang][NewPM] Fixing remaining -O0 tests that are broken under new PM

[clang][NewPM] Fixing remaining -O0 tests that are broken under new PM

- CodeGen/flatten.c will fail under new PM becausec the new PM AlwaysInliner
  seems to intentionally inline functions but not call sites marked with
  alwaysinline (D23299)
- Tests that check remarks happen to check them for the inliner which is not
  turned on at O0. These tests just check that remarks work, but we can make
  separate tests for the new PM with -O1 so we can turn on the inliner and
  check the remarks with minimal changes.

Differential Revision: https://reviews.llvm.org/D62225

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@363846 91177308-0d34-0410-b5e6-96231b3b80d8