Fix GCD calculation for Boolean reified linear constraints. #54

Job	Run time
build-cmake (windows-latest)	13m 14s
build-cmake (macos-latest)	5m 12s
build-autoconf (ubuntu-latest)	8m 3s
build-cmake (ubuntu-latest)	10m 57s
build-autoconf (macos-latest)	4m 42s
	42m 8s

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