Copy the set_tls_base flag when forking.
Copy the set_tls_base flag when forking.

This enables the linux_child_return bits that set the TLS base in the
newly forked process.

Before this, processes that had the flag set would get a null pointer and
segfault when trying to access the TLS area.

Chased down and fixed by me. Turned into a proper one line diff by guenther@.

orumin/openbsd-efivars,orumin/openbsd-efivars,orumin/openbsd-efivars,orumin/openbsd-efivars