Remove $FreeBSD$: one-line sh pattern

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

Turn off gcc's uninitialized warnings for this code. They
can be fixed, but really do appear to be false alarms.

Import HyperV Key-Value Pair (KVP) driver and daemon code by Microsoft,
many thanks for their continued support of FreeBSD.

While I'm there, also implement a new build knob, WITHOUT_HYPERV to
disable building and installing of the HyperV utilities when necessary.

The HyperV utilities are only built for i386 and amd64 targets.

This is a stable/10 candidate for inclusion with 10.1-RELEASE.

Submitted by: Wei Hu <weh microsoft com>
MFC after: 1 week