feat: add perf walltime support#13

not-matthias wants to merge 4 commits intomainCodSpeedHQ/codspeed-cpp:mainfrom

cod-918-perf-doesnt-work-for-cpp-codspeedCodSpeedHQ/codspeed-cpp:cod-918-perf-doesnt-work-for-cpp-codspeedCopy head branch name to clipboard