Bug#984231: mathicgb: ftbfs with GCC-11

[Torrance, Douglas]

Control: forwarded -1 https://github.com/Macaulay2/mathicgb/issues/25

Matthias Klose writes:

> The package fails to build in a test rebuild on at least amd64 with
> gcc-11/g++-11, but succeeds to build with gcc-10/g++-10. The
> severity of this report will be raised before the bookworm release,
> so nothing has to be done for the bullseye release.

Thanks for the report!  Forwarded upstream.