Revert "build-sys: silence make by default or V=0"

This reverts commit 42a77f1c.

The primary intention of this change was to silence messages
like

  make[1]: '/home/berrange/src/virt/qemu/capstone/libcapstone.a' is up to date.

which we get when calling make recursively with explicit
targets.

The problem is that this change affected every make target,
not merely the targets that triggered these "is up to date"
messages. As a result any targets that were not invoking
commands via "$(call quiet-command ...)" suddenly become
silent. This is particularly bad for "make install" which
now appears todo nothing.

Rather than go through every make rule and try to identify
places where we now need to explicitly print a message to
show work taking place, just revert the change.

To address the original problem of silencing "is up to date"
messages, we simply add --quiet to the SUBDIR_MAKEVARS
variable, so it only affects us on recursive make calls.

Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
Message-Id: <20180123164718.12714-2-berrange@redhat.com>
Tested-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>