travis-ci: Enable/disable more features in various builds

travis-ci: Enable/disable more features in various builds

In the debug build, enable features that are off by default. In the
reduced build, explicitly disable features, some of which are
on by default. In the legacy build, check that we can compile the
default feature-set without inotify, dnotify, systemd, etc.

Reviewed-by: Philip Withnall <withnall@endlessm.com>
[smcv: Rebase onto 1.13.x branch, fix minor conflicts]
Signed-off-by: Simon McVittie <smcv@collabora.com>
Bug: https://bugs.freedesktop.org/show_bug.cgi?id=101354
(cherry picked from commit 3c031ef5aa1f7f53c6344781cb38b78abe44dc96)