Splitting up a library without breaking ABI?

[Stef Walter <stefw collabora co uk>]

The libgcr library lives inside the gnome-keyring project. I'd like to
split it out into its own module, which is easy enough.

But at the same time I'd like to split it into two libraries: one with a
GTK+ dependency (UI bits), and the other without. I'm not a release
'superstar', hence the question:

Is there a way to split a library into two without breaking ABI?

The current pkg-config file library is libgcr-3.so. Would it work to
have libgcr-3.so depend on the two new libraries (eg: libgcr-base-3.so,
libgcr-gtk-3.so).

Or is this just not worth it, and I'll just worry about preserving API
backwards compatibility in such a split and not ABI?

Cheers,

Stef