To use the DLLs in Visual Studio, please use the linker option /OPT:NOREF.

You can change this setting at Project Properties -> Configuration Properties
-> Linker -> Optimization -> References -> Keep Unreferenced Data (/OPT:NOREF).

This is the default in Debug mode, but Release mode usually sets /OPT:REF
instead.

The reason for this is a bug in binutils/dlltool; see
http://sourceware.org/bugzilla/show_bug.cgi?id=12633

This will probably be fixed in future versions.
