The plugin should explicitly link to gmodule-2.0:

/bin/sh ../../../libtool --tag=CXX   --mode=link g++ -DGTK -fomit-frame-pointer -fmessage-length=0 -O2 -Wall -D_FORTIFY_SOURCE=2 -fstack-protector -funwind-tables -fasynchronous-unwind-tables -g   -o test-scintilla test_scintilla-test-scintilla.o libanjuta-scintilla.la
libtool: link: g++ -DGTK -fomit-frame-pointer -fmessage-length=0 -O2 -Wall -D_FORTIFY_SOURCE=2 -fstack-protector -funwind-tables -fasynchronous-unwind-tables -g -o test-scintilla test_scintilla-test-scintilla.o  ./.libs/libanjuta-scintilla.a -lanjuta-3 -lgdl-3 -lgtk-3 /usr/lib/libxml2.so -ldl -lz -lgdk-3 -latk-1.0 -lgio-2.0 -lpangocairo-1.0 -lgdk_pixbuf-2.0 -lcairo-gobject -lpango-1.0 -lcairo -lgobject-2.0 -lgthread-2.0 -lrt -lglib-2.0 -pthread
/usr/lib/gcc/i586-suse-linux/4.6/../../../../i586-suse-linux/bin/ld: ./.libs/libanjuta-scintilla.a(PlatGTK.o): undefined reference to symbol 'g_module_close'
/usr/lib/gcc/i586-suse-linux/4.6/../../../../i586-suse-linux/bin/ld: note: 'g_module_close' is defined in DSO /usr/lib/libgmodule-2.0.so.0 so try adding it to the linker command line
/usr/lib/libgmodule-2.0.so.0: could not read symbols: Invalid operation
collect2: ld returned 1 exit status