CMake

made deletions parallel and faster yay #1117

Job	Run time
full-build (ubuntu-latest, "-DL0_SAMPLING")	19s
full-build (ubuntu-latest, "-DNO_EAGER_DSU")	21s
full-build (ubuntu-latest, "")	16s
full-build (ubuntu-20.04, "-DL0_SAMPLING")	29s
full-build (ubuntu-20.04, "-DNO_EAGER_DSU")	32s
full-build (ubuntu-20.04, "")	31s
	2m 28s

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