This also builds the agent statically with libsysprof_static_dep since
we'd need that to avoid installing libsysprof when that isn't wanted.
It also ensures the LD_PRELOAD libraries are installed for use by the
agent.
This is all aimed at making it so that sysprof can be built as a
subproject within GLib, with only `libsysprof-capture-4.a` being
produced as output.
Signed-off-by: Philip Withnall <withnall@endlessm.com>
