This routine and krb5_build_principal_va perform
the same function. krb5_build_principal takes
a variable-length argument list, which is added to the principal
data being built.
Both functions take a realm name realm,
realm name length rlen, and a list of null-terminated
strings, and fill in a pointer to a principal structure principal,
making it point to a structure representing the named principal.
The last string must be followed in the argument list by a NULL