Add benchmark comparison
    
    Create a new package glibc-benchtests with the benchmark binaries that
    one may download and run to benchmark glibc for their machine.  More
    importantly, the glibc-bench-compare and bench.mk scripts can run
    benchmarks and compare performance of two arbitrary glibc versions as
    long as both versions have the glibc-benchtests package.
    
    Usage:
    
    Scenario 1: Compare two build numbers, e.g.:
    
        /usr/libexec/glibc-benchtests/glibc-bench-compare 2.20-1.fc21 2.21.90-11.fc22
    
    If a second build is omitted, comparison is done with the currently
    installed glibc.
    
    Scenario 2: Compare two downloaded rpms - only glibc, glibc-benchtests
    and glibc-common are needed for both versions.  e.g.:
    
        /usr/libexec/glibc-benchtests/glibc-bench-compare -p <dir1> <dir2>