release/vm: add a WITHOUT_QEMU option

[brooks]

Summary

This option disables trying to build a qemu-<target>-static and simply
doesn't do any of the operations that rely on it. At a glance, all
appear to be useful, but not essential to building simple images without
packages.

Disable all CLOUDWARE variants that require pkg when WITHOUT_QEMU is set
as this currently requires qemu support.

[brooks]

• Don't require WITHOUT_QEMU to have a value
• Rebase

[brooks]

Implement suggetions from @jrtc27

• Use shell variable substitutions instead of temporaries
• Use DESTDIR-relative paths in makefs calls

[brooks]

In D49310#1124766, @brooks wrote:

Implement suggetions from @jrtc27

• Use shell variable substitutions instead of temporaries
• Use DESTDIR-relative paths in makefs calls

Sigh, somehow the fix applied to the wrong commit. Will reconstruct and update.

[brooks]

Restore to previous version