The engines are built as static modules and not dynamic as they should.
Removing acinclude.m4 before running libtoolize fixes the problem.
Any reason for using automake1.4? It builds fine with automake-1.5-8.
Next build of gtk-engines should fix this bug.
The reason for using automake-1.4 is that there is no reason to
deviate from the upstream package and risk incompatiblities.