You mean it complains at run time (where "it" is glib in this case).
This has the look of what would happen if you had more than one copy
of the library around. libspreadsheet in this case, so half the code sees
one version of GnmCellCombo and the other half see the other.
The warning is saving you some severe hair pulling.
Solution? Some combination of "make clean", "make install", and manually
checking for multiple versions.