Apparently, I made a mistake: I was editing makefile.preamble in GWorkspace, while changingthe linker parameters in ProjectCenter. When linking, it was certainly not using the file version with ADITIONAL_LDFLAGS += ADDITIONAL_NATIVE_LIBS += EOControl EOAccess EOInterface that I found later, because that gave errors. The solution was to add -lEOControl -lEOAccess -lEOInterface as linker flags, probably what Germán had in mind.
Sorry for the fuzz.
Another remark,nothing important, a small inconsistency I found whle fooling around with the libraries : when I manually add the libraries with ADDITIONAL_LDFLAGS, I can use ADITIONAL_LDFLAGS += ADDITIONAL_NATIVE_LIBS += EOControl EOAccess EOInterface to make it work
When doing the same with ADDITIONAL_GUI_LIBS, I have to use
ADDITIONAL_GUI_LIBS += -lEOControl -lEOAccess -lEOInterface or I get linker errors
Edwin Ancaer