Tinderbox has historically found dependencies of ports by
running make -Vx_DEPENDS in the port's directory.  Unfortunately,
this causes the host's environment and filesystems to be used, where
the calculations should be inside the build jails.

This patch causes the dependencies to be calculated inside the jails,
using chroot(8), and was extensively tested by Olli Hauer, as well as
Bernhard Froehlich and Jase Thew (thanks very much!)

Approved by:	marcus
Set CC and CXX to point to GNU versions of legacy OSes.  I strongly
suspect this is needed and won't break anything.
Use pkg-static instead of pkg to avoid a chick and egg condition.

Submitted by:	ohauer
Update to 4.1.0.
Fix enterBuild by adding a missing declaration of ${tc} and correcting
the fully-qualified path to the port directory.

Submitted by:	Anes Mukhametov <anes@anes.su>