[llvm-exegesis] Add a flag to disable libpfm even if present.

Summary: Fixes PR37053.

Reviewers: uabelho, gchatelet

Subscribers: mgorny, tschuett, llvm-commits

Differential Revision: https://reviews.llvm.org/D45436

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@329781 91177308-0d34-0410-b5e6-96231b3b80d8
5 files changed