tests: Fix function signatures

CONTRIBUTING.md

tests/alloca.c

tests/args.c

tests/arpainet.c

tests/assert.c

tests/constructor.c

tests/ctype.c

tests/destructor.c

tests/dirent/main.c

tests/dirent/scandir.c

tests/error.c

tests/fcntl/create.c

tests/fcntl/fcntl.c

tests/fnmatch.c

tests/libgen.c

tests/locale.c

tests/math.c

tests/netdb/netdb.c

tests/pwd.c

tests/regex.c