sysdeps/generic/libc.abilist and __libc_single_threaded

[Joseph Myers]

sysdeps/generic/libc.abilist is nonempty: it contains only the symbol 
__libc_single_threaded, added by:

commit 706ad1e7af37be1d25fc2359bda006d31fe0d11b
Author: Florian Weimer <fweimer@redhat.com>
Date:   Wed May 20 15:40:35 2020 +0200

    Add the __libc_single_threaded variable

Should this file really contain this symbol, or should it be an empty file 
like all the other sysdeps/generic/*.abilist, given that all glibc ABIs 
need their own libc.abilist for libc ABI tests to pass?

-- 
Joseph S. Myers
joseph@codesourcery.com