[glibc] nptl: Add missing placeholder abi symbol from nanosleep move

[Florian Weimer]

* Adhemerval Zanella:

> Is there a way to force linker to add the .gnu.version_d from the linker
> version map without actually requiring the add this place holder symbol?

Oh, and I looked at this and binutils does strange things if you have a
symbol version that does not have any symbols attached to it, but is
referenced by a higher version number.  It creates a weak symbol
definition, and that's rather uncharted territory.

Thanks,
Florian