This fixes building of the dll on Cygwin.

--- ./builds/unix/unix-cc.in~	2003-11-09 09:37:13.000000000 +0100
+++ ./builds/unix/unix-cc.in	2007-05-30 14:34:33.000000000 +0200
@@ -93,7 +93,7 @@
 # Library linking
 #
 LINK_LIBRARY = $(LIBTOOL) --mode=link $(CCraw) -o $@ $(OBJECTS_LIST) \
-                          -rpath $(libdir) -version-info $(version_info) \
+                          -rpath $(libdir) -no-undefined -version-info $(version_info) \
                           $(LDFLAGS)