This fix is needed to work around linker-errors such as
undefined reference to `__libc_csu_fini'
which I got in almost every derivation which is part of stage2. The
reasoning behind this is that the startup-code was simplified[1] and
thus `__libc_csu_fini` doesn't exist anymore.
A workable solution is to use a newer libc which properly links in
stage3. And actually this seems expected given the rationale for stage3:
# Construct a third stdenv identical to the 2nd, except that this
# one uses the rebuilt Glibc from stage2. It still uses the recent
# binutils and rest of the bootstrap tools, including GCC.
So this patch basically overrides the libraries inside `gcc-unwrapped` -
which is basically the bootstrap tools and thus also contains the libc
used in stage3 - with the shared objects from the freshly built libc
from stage2.
[1] https://sourceware.org/pipermail/libc-alpha/2021-March/123079.html
Maximilian Bosch
7459a4021c