CMake

Simplify datetimeFromNumber code #118

Job	Run time
build (ubuntu-latest, Debug, static, 5.12, x86_64)	38s
build (ubuntu-latest, Debug, static, 6.6.0, x86_64;arm64)	1m 0s
build (ubuntu-latest, Debug, shared, 5.12, x86_64)	40s
build (ubuntu-latest, Debug, shared, 6.6.0, x86_64;arm64)	56s
build (ubuntu-latest, Release, static, 5.12, x86_64)	1m 51s
build (ubuntu-latest, Release, static, 6.6.0, x86_64;arm64)	1m 5s
build (ubuntu-latest, Release, shared, 5.12, x86_64)	42s
build (ubuntu-latest, Release, shared, 6.6.0, x86_64;arm64)	1m 10s
build (windows-latest, Debug, static, 5.12, x86_64)	1m 33s
build (windows-latest, Debug, static, 6.6.0, x86_64;arm64)	1m 59s
build (windows-latest, Debug, shared, 5.12, x86_64)	1m 16s
build (windows-latest, Debug, shared, 6.6.0, x86_64;arm64)	1m 12s
build (windows-latest, Release, static, 5.12, x86_64)	1m 12s
build (windows-latest, Release, static, 6.6.0, x86_64;arm64)	2m 17s
build (windows-latest, Release, shared, 5.12, x86_64)	1m 18s
build (windows-latest, Release, shared, 6.6.0, x86_64;arm64)	2m 8s
build (macos-latest, Debug, static, 5.12, x86_64)	30s
build (macos-latest, Debug, static, 6.6.0, x86_64;arm64)	1m 15s
build (macos-latest, Debug, shared, 5.12, x86_64)	27s
build (macos-latest, Debug, shared, 6.6.0, x86_64;arm64)	1m 11s
build (macos-latest, Release, static, 5.12, x86_64)	33s
build (macos-latest, Release, static, 6.6.0, x86_64;arm64)	1m 11s
build (macos-latest, Release, shared, 5.12, x86_64)	32s
build (macos-latest, Release, shared, 6.6.0, x86_64;arm64)	1m 11s
	27m 47s

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