Print a warning if the benchmark is running inside a cgroup with a me… #64

Job	Run time
Build/Test ubuntu-latest clang fastbuild	42m 43s
Build/Test arm-ubuntu-arm-22.04-16core clang fastbuild	11m 27s
Build/Test ubuntu-latest gcc fastbuild	27m 56s
Build/Test ubuntu-latest clang opt	1h 6m 51s
Build/Test ubuntu-latest gcc opt	40m 55s
Build/Test arm-ubuntu-arm-22.04-16core gcc opt	8m 20s
Build/Test arm-ubuntu-arm-22.04-16core clang opt	9m 19s
Build/Test arm-ubuntu-arm-22.04-16core gcc fastbuild	8m 28s
	3h 35m 59s

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