Bug#206531: #206531: Problems building d-i after upgrading Sid chroot

[Philip Blundell <pb@nexus.co.uk>]

It appears that the problem here is caused by dso_handle.os being
omitted from the reduced libc.  This leaves __dso_handle as an undefined
weak reference.  Unfortunately, for a shared build, glibc assumes that
this symbol will always be available and elides the check for its
existence in thread_atfork().  Consequently, the reduced libc blows up
with a null dereference in ptmalloc_init.

I added a hack to mklibs 0.1.12 to force the inclusion of this symbol in
the reduced libc.so, which seems to be enough to get debian-installer
working again.

p.