[PassManagerBuilder] Add option for interleaved loops, for loop vectorize.

Summary:
Match NewPassManager behavior: add option for interleaved loops in the
old pass manager, and use that instead of the flag used to disable loop unroll.
No changes in the defaults.

Reviewers: chandlerc

Subscribers: mehdi_amini, jlebar, dmgreen, hsaito, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D61030

llvm-svn: 359615