GPUMeter code refactor & macOS support #4830

Job	Run time
build-netbsd-latest-gcc	2m 52s
build-dragonflybsd-latest-gcc	2m 34s
build-freebsd-latest-clang	2m 4s
build-macos-latest-clang	48s
build-openbsd-latest-clang	2m 21s
build-solaris-latest-gcc	3m 43s
build-ubuntu-latest-clang-analyzer	1m 19s
build-ubuntu-latest-clang-sanitizer	1m 8s
build-ubuntu-latest-full-featured-clang	1m 55s
build-ubuntu-latest-full-featured-gcc	51s
build-ubuntu-latest-minimal-clang	2m 12s
build-ubuntu-latest-gcc-static	52s
build-ubuntu-latest-minimal-gcc	39s
build-ubuntu-latest-pcp	33s
lint-pcp-config	3s
lint-whitespace	3s
	23m 57s

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