[ThinLTO] Add testing of new summary index format to a couple CFI tests

Summary:
Adds testing of combined index summary entries in disassembly format
to CFI tests that were already testing the bitcode format.

Depends on D46699.

Reviewers: pcc

Subscribers: mehdi_amini, inglorion, eraman, cfe-commits

Differential Revision: https://reviews.llvm.org/D46700

llvm-svn: 333966