[X86][BtVer2][MCA][NFC] Add CMPEQ dependency-breaking one-idioms tests

Summary: As per `Agner's Microarchitecture doc
(21.8 AMD Bobcat and Jaguar pipeline - Dependency-breaking instructions)`,
these, like zero-idioms, are dependency-breaking,
although they produce ones and still consume resources.

FIXME: as discussed in D48877, llvm-mca handling is broken for these.

Reviewers: andreadb

Reviewed By: andreadb

Subscribers: gbedwell, RKSimon, llvm-commits

Differential Revision: https://reviews.llvm.org/D48876

llvm-svn: 336292