Simplify libatomic detection #34

Job	Run time
linux_gcc_sanitizers	2m 18s
linux_gcc_valgrind	1m 7s
linux_clang (ubuntu-latest, Debug)	3m 27s
linux_clang (ubuntu-latest, Release)	1m 41s
linux_gcc (ubuntu-latest, Debug)	4m 30s
macos_clang (macos-latest, Debug)	4m 29s
windows_mingw64 (windows-latest, Debug)	5m 32s
linux_gcc (ubuntu-latest, Release)	2m 28s
macos_clang (macos-latest, Release)	2m 29s
windows_mingw64 (windows-latest, Release)	2m 53s
windows_msvc2022	1m 54s
	32m 48s

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