cksum: Improve the GNU compat #3028

Job	Run time
Build the fuzzers	2m 3s
Run the fuzzers (fuzz_test, true)	2m 20s
Run the fuzzers (fuzz_date, false)	1m 32s
Run the fuzzers (fuzz_expr, true)	2m 31s
Run the fuzzers (fuzz_printf, false)	1m 18s
Run the fuzzers (fuzz_echo, true)	2m 27s
Run the fuzzers (fuzz_seq, false)	1m 23s
Run the fuzzers (fuzz_sort, false)	1m 35s
Run the fuzzers (fuzz_wc, false)	1m 36s
Run the fuzzers (fuzz_cut, false)	1m 17s
Run the fuzzers (fuzz_split, false)	1m 43s
Run the fuzzers (fuzz_tr, false)	1m 46s
Run the fuzzers (fuzz_env, false)	1m 16s
Run the fuzzers (fuzz_parse_glob, true)	2m 19s
Run the fuzzers (fuzz_parse_size, true)	2m 17s
Run the fuzzers (fuzz_parse_time, true)	2m 22s
Run the fuzzers (fuzz_seq_parse_number, true)	2m 10s
	31m 55s

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