[RFC] elf: Implement filtering of symbols historically defined in libpthread

[Florian Weimer]

* H. J. Lu:

> Why re-linking is needed for the binary executable test?

I don't want us to bundle the sources of an old glibc version, just to
comply with the LGPL requirements for one single test (or talk to legal
folks to figure out if this is required).

Thanks,
Florian