[llvm-exegesis] Improve Register Setup (roll forward of D51856).

Summary:
Added function to set a register to a particular value + tests.
Add EFLAGS test, use new setRegTo instead of setRegToConstant.

Reviewers: courbet, javed.absar

Subscribers: llvm-commits, tschuett, mgorny

Differential Revision: https://reviews.llvm.org/D52297

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@342644 91177308-0d34-0410-b5e6-96231b3b80d8
16 files changed