Fix warnings

Fix warnings

reqname, bindaddr, request_addr, desthost and orighost to be exhaustive.

This function is used when USE_VFORK is unset.

Changing checkusername()'s username argument into char * as well.

Data is usually represented as "unsigned char *" like genrandom().

error: ‘noreturn’ function does return [-Werror]

abort() is a noreturn function while raise() is not.

And because crypt_argchk() is flagged as __attribute__(noreturn), abort()
appears to be a better condidate.

This compilation warning has probably been introduced by commit
1809f741.