Update to glibc copyright assignment policy

[Carlos O'Donell via Libc-alpha <libc-alpha@sourceware.org>]

glibc was created as part of the GNU Project but has grown to operate
as an autonomous project.

The glibc stewards have decided to relax the requirement to assign
copyright for all changes to the Free Software Foundation. glibc will
continue to be developed, distributed, and licensed under the GNU
Lesser General Public License v2.1 or any later version as published
by the Free Software Foundation.  This change is consistent with the
practices of many other major Free Software projects, such as the
Linux kernel, and GCC [1].

Contributors who have an FSF Copyright Assignment don't need to change
anything.  Contributors who wish to utilize the Developer Certificate
of Origin[2] should add a Signed-off-by message to their commit
messages.

The changes to accept patches with or without FSF copyright assignment
will be effective after August 2nd, and will apply to all open
branches. Code shared with other GNU packages via Gnulib will continue
to require assignment to the FSF.

The glibc stewards continue to affirm the principles of Free Software,
and that will never change.

Signed,
Ryan Arnold
Paul Eggert
Jakub Jelinek
Maxim Kuvyrkov
Joseph Myers
Carlos O'Donell

[1] https://gcc.gnu.org/pipermail/gcc/2021-June/236182.html
[2] https://developercertificate.org/