Fix #75696: posix_getgrnam fails to print details of group

Fix #75696: posix_getgrnam fails to print details of group

According to the POSIX specification of `getgrnam_r()` the result of
`sysconf(_SC_GETGR_R_SIZE_MAX)` is an initial value suggested for the
size of the buffer, and `ERANGE` signals that insufficient storage was
supplied.  So if we get `ERANGE`, we try again with a buffer twice as
big, and so on, instead of failing.