Generalize mmap #441

Job	Run time
build (mathcomp/mathcomp-dev:rocq-prover-9.0)	16m 19s
build (mathcomp/mathcomp:2.4.0-coq-8.20)	3m 50s
build (mathcomp/mathcomp:2.4.0-rocq-prover-9.0)	3m 29s
build (mathcomp/mathcomp-dev:rocq-prover-dev)	3m 55s
	27m 33s

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