Add strto[iu]_() and strtou_noneg().

[alejandro-colomar]

This is in preparation of a rework of get[u]long().

[alejandro-colomar]

Link: https://lists.sr.ht/~hallyn/shadow/%3CZZoQDms6Sv6e5SPE%40debian%3E
Link: https://lists.freedesktop.org/archives/libbsd/2024-January/000384.html
Link: https://gnats.netbsd.org/cgi-bin/query-pr-single.pl?number=57828
Link: http://cvsweb.netbsd.org/bsdweb.cgi/src/common/lib/libc/stdlib/_strtoi.h?only_with_tag=MAIN
Link: http://cvsweb.netbsd.org/bsdweb.cgi/src/common/lib/libc/stdlib/_strtoi.h.diff?r1=1.2&r2=1.3&only_with_tag=MAIN

NetBSD has modified their APIs strtoi(3) and strtou(3) after my bug report, so our implementation will be fully compatible with theirs. libbsd will also adopt that behavior soon. However, for now, let's use our own definitions.

[alejandro-colomar]

v2 changes:

• Rebase to master

$ git range-diff master..gh/strtou_ shadow/master..strtou_ 
1:  619e0441 = 1:  7d7f7717 lib/atoi/strtoi.[ch]: strtoi_(), strtou_(): Add functions
2:  08dc5030 = 2:  7366080a tests/unit/test_atoi_strtoi.c: Test strtoi_()
3:  387d37a7 = 3:  99a7bc89 tests/unit/Makefile.am: tfix
4:  6a854e5b = 4:  324bce7b lib/atoi/strtou_noneg.[ch]: Add strtou_noneg()
5:  027f51e4 = 5:  b08d6260 tests/unit/test_atoi_strtoi.c: Test strtou_noneg()

[alejandro-colomar]

v2b changes:

• Rebase to master

$ git range-diff master..gh/strtou_ shadow/master..strtou_ 
1:  7d7f7717 = 1:  1aebf7b4 lib/atoi/strtoi.[ch]: strtoi_(), strtou_(): Add functions
2:  7366080a = 2:  74096f8e tests/unit/test_atoi_strtoi.c: Test strtoi_()
3:  99a7bc89 = 3:  0c309e1b tests/unit/Makefile.am: tfix
4:  324bce7b = 4:  03f17ef8 lib/atoi/strtou_noneg.[ch]: Add strtou_noneg()
5:  b08d6260 = 5:  570aa4ca tests/unit/test_atoi_strtoi.c: Test strtou_noneg()