[ORE] Move loop invariant ORE checks outside the PM loop.

Summary:
This takes 22ms out of ~20s compiling sqlite3.c because we call it
for every unit of compilation and every pass.

Reviewers: paquette, anemet

Subscribers: mehdi_amini, llvm-commits

Differential Revision: https://reviews.llvm.org/D49586

llvm-svn: 337654