contrib/bc: update to version 4.0.1

This update adds a flush() of the output buffer to the bc print
command.

(cherry picked from commit 8ea9013512494c9f035afa1ffa1e199b44c7904f)

Synch index of contrib/bc with what is in workdir after cloning.

From a workdir perspective this should be a no-op.
See also:
https://lists.freebsd.org/pipermail/freebsd-current/2021-April/079569.html

(cherry picked from commit a0358e3d5184950b4316f105eb292cbafdea208b)