Just updating glibmm's buildlink3.mk is not good enough. That causes a new 
error for me:

	ERROR: glibmm is not installed; can't buildlink files.

It is installed.

Bumping the BUILDLINK_ABI_DEPENDS.libsigcpp also does not help.

Bumping BUILDLINK_API_DEPENDS.gtkmm should do it in addition to the 
BUILDLINK_API_DEPENDS.glibmm, but that means I have to reinstall three new 
packages (for no real API reason) just because one was renamed.

Any advice?

A third idea is to get the new buildlink3.mk file for libsigc++ to know 
about the previous PKGNAME and maybe use it?

  Jeremy C. Reed