CMake

Simplify datetimeFromNumber code #119

Job	Run time
build (ubuntu-latest, Debug, static, 5.12, x86_64)	46s
build (ubuntu-latest, Debug, static, 6.6.0, x86_64;arm64)	1m 4s
build (ubuntu-latest, Debug, shared, 5.12, x86_64)	1m 0s
build (ubuntu-latest, Debug, shared, 6.6.0, x86_64;arm64)	1m 9s
build (ubuntu-latest, Release, static, 5.12, x86_64)	48s
build (ubuntu-latest, Release, static, 6.6.0, x86_64;arm64)	1m 6s
build (ubuntu-latest, Release, shared, 5.12, x86_64)	49s
build (ubuntu-latest, Release, shared, 6.6.0, x86_64;arm64)	1m 0s
build (windows-latest, Debug, static, 5.12, x86_64)	1m 24s
build (windows-latest, Debug, static, 6.6.0, x86_64;arm64)	1m 42s
build (windows-latest, Debug, shared, 5.12, x86_64)	1m 26s
build (windows-latest, Debug, shared, 6.6.0, x86_64;arm64)	1m 43s
build (windows-latest, Release, static, 5.12, x86_64)	1m 27s
build (windows-latest, Release, static, 6.6.0, x86_64;arm64)	1m 50s
build (windows-latest, Release, shared, 5.12, x86_64)	55s
build (windows-latest, Release, shared, 6.6.0, x86_64;arm64)	1m 52s
build (macos-latest, Debug, static, 5.12, x86_64)	43s
build (macos-latest, Debug, static, 6.6.0, x86_64;arm64)	1m 27s
build (macos-latest, Debug, shared, 5.12, x86_64)	50s
build (macos-latest, Debug, shared, 6.6.0, x86_64;arm64)	1m 6s
build (macos-latest, Release, static, 5.12, x86_64)	31s
build (macos-latest, Release, static, 6.6.0, x86_64;arm64)	1m 11s
build (macos-latest, Release, shared, 5.12, x86_64)	33s
build (macos-latest, Release, shared, 6.6.0, x86_64;arm64)	1m 11s
	27m 33s

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