[llvm-mca] Compare multiple files

Script (llvm-mca-compare.py) uses llvm-mca tool to print
statistics in console for multiple files.
Script requires specified --llvm-mca-binary option (specified
relative path to binary of llvm-mca).
Options: --args [="-option1=<arg> -option2=<arg> ..."], -v or -h can also be used.

The script is used as follows:
$ llvm-project/llvm/utils/llvm-mca-compare.py file1.s --llvm-mca-binary=build/bin/llvm-mca

Patch by Milica Matic <Milica.Matic@syrmia.com>

Differential Revision: https://reviews.llvm.org/D115138