Remove $FreeBSD$: one-line sh pattern

Remove /^\s*#[#!]?\s*\$FreeBSD\$.*$\n/

usr.bin/gh-bc: update Makefiles for version 6.2.2

The sources of this program are in contrib/bc, but built using the
Makefiles touched in this commit, which had to be adapted to comply
with changed made to the build system of this software, which is
not used when building in the base system.

usr.bin/ghä-bc, contrib/bc: update to version 5.0.0

Merge commit 2f57ecae4b98e76e5d675563785a7e6c59c868c4

This is a new major release with a number of changes and extensions:

- Limited the number of temporary numbers and made the space for them
static so that allocating more space for them cannot fail.
- Allowed integers with non-zero scale to be used with power, places,
and shift operators.
- Added greatest common divisor and least common multiple to lib2.bc.
- Made bc and dc UTF-8 capable.
- Added the ability for users to have bc and dc quit on SIGINT.
- Added the ability for users to disable prompt and TTY mode by
environment variables.
- Added the ability for users to redefine keywords.
- Added dc's modular exponentiation and divmod to bc.
- Added the ability to assign strings to variables and array elements
and pass them to functions in bc.
- Added dc's asciify command and stream printing to bc.
- Added bitwise and, or, xor, left shift, right shift, reverse,
left rotate, right rotate, and mod functions to lib2.bc.
- Added the functions s2u(x) and s2un(x,n), to lib2.bc.

MFC after: 1 week

Connect the tests provided with the new bc and dc

The tests compare the command output (including of error cases) with the
expected output and exit code.

Not all tests are executed, since some expect to have a known good bc and
dc binary installed and compare results of large amounts of generated data
being processed by both versions to test for regressions.