Support hash size that's not std::size_t #478

Job	Run time
build-spm	17s
build	19m 29s
docs	1m 8s
check (Debug, gnu-6, 14)	2m 50s
check (Debug, gnu-7, 14)	2m 58s
check (Debug, llvm-5, 14)	2m 39s
check (Debug, llvm-6, 14)	2m 48s
check (Release, gnu-6, 14)	3m 50s
check (Release, gnu-7, 14)	3m 44s
check (Release, llvm-5, 14)	4m 8s
check (Release, llvm-6, 14)	4m 13s
check (Debug, gnu-9, 14, coverage)	3m 38s
check (Debug, gnu-8, 17)	3m 10s
check (Debug, llvm-9, 17, fuzzers)	4m 10s
check (Debug, gnu-11, 20)	3m 20s
check (Debug, llvm-13, 20)	3m 15s
check (Debug, llvm-8, 14, sanitize)	3m 57s
check (Release, gnu-9, 14, benchmark)	19m 15s
check (Release, llvm-10, 14, benchmark)	19m 32s
	1h 48m 21s

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