[bc] Update to version 4.0.0

This version fixes an issue (missing pop of top-of-stack value in the
"P" command of the dc program).

This issue did not affect the bc program, since it does not use dc as
an back-end to actually perform the calculations as was the case with
the traditional bc and dc programs.

The major number has been bumped due to Windows support that has been
added to this version. It does not correspond to a major change that
might affect FreeBSD.

MFC after: 3 days