Providing a remote will limit build's pull/push remote actions to
the given remote specifically, ignoring those defined via user or
project configuration.

Add --remote, -r option to bst build, inline with pull & push

See merge request !1119

In order to support use of roaring bitmaps in the loader, we need to
depend on it here.

Signed-off-by: Daniel Silverstone <daniel.silverstone@codethink.co.uk>

The dependency cache in LoadElement causes the peak RAM consumption of
the loader to be exceedingly large, upwards of 25GB for a test of a
Debian stack.  By switching from the old dict cache to a roaring bitmap
based cache, we reduce the cost of the loader cache in RAM terms to
around 5.5GB for the same stack, which makes it plausible for the short
term.

Signed-off-by: Daniel Silverstone <daniel.silverstone@codethink.co.uk>