Added processor group support for >64 processors#387

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techvintage wants to merge 3 commits intoPOV-Ray:masterfrom

techvintage:ProcessorGroups

Commits on Dec 11, 2019

Added processor group support for >64 processors
techvintage
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Commits on Dec 19, 2019

Ensure windows specific code does not run on Linux or Mac builds
techvintage
committed
More changes to ensure windows specific code still builds with
techvintage
committed