Remove residual blank line at start of Makefile

This is a residual of the $FreeBSD$ removal.

MFC After: 3 days (though I'll just run the command on the branches)
Sponsored by: Netflix

Remove $FreeBSD$: one-line sh pattern

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

wc: Clean up and modernize.

* Drop <err.h>, which is unnecessary since we use libxo.

* As per POSIX, report an error if output fails.

* Fix some type mismatches.

* Use bool instead of int where a

wc: Clean up and modernize.

* Drop <err.h>, which is unnecessary since we use libxo.

* As per POSIX, report an error if output fails.

* Fix some type mismatches.

* Use bool instead of int where appropriate.

* Avoid repeatedly checking for a null filename.

* Miscellaneous other tidying.

* Add tests (partly derived from work performed by SHENG-YI HONG <i19780219111@kimo.com>).

Sponsored by: Klara, Inc.
Reviewed by: kevans
Differential Revision: https://reviews.freebsd.org/D38496

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