Can link against a dll using CMake but not qmake - c++

Question

I want to build a simple Qt project on Windows which consists of one main.cpp file and a dll.
I have no problems with building it using CMake:
project(app)
cmake_minimum_required(VERSION 2.6.0)
find_package(Qt4 REQUIRED QtCore QtGui QtXml)
...
add_executable(app main.cpp)
target_link_libraries(app ${QT_LIBRARIES} my_dll.dll)
Then I try to build it using qmake:
...
SOURCES += main.cpp
win32:{
LIBS += -L"my_dll.dll"
}
In this case the build fails and I get linker errors like undefined reference to 'my_function#8', where my_function is a function in my_dll.dll.
When I open my_dll.dll with Dependency Walker I can see that all function names are not decorated. I don't know why qmake tries to resolve function names with '#8' at the end.
This is what CMake writes to the log on linking:
C:\MinGW\bin\g++.exe -g -Wl,--whole-archive CMakeFiles\app.dir/objects.a -Wl,--no-whole-archive -o app.exe -Wl,--out-implib,libapp.dll.a -Wl,--major-image-version,0,--minor-image-version,0 C:\QT\2010.02.1\qt\lib\libQtGuid4.a C:\QT\2010.02.1\qt\lib\libQtXmld4.a C:\QT\2010.02.1\qt\lib\libQtCored4.a -l,my_dll -lkernel32 -luser32 -lgdi32 -lwinspool -lshell32 -lole32 -loleaut32 -luuid -lcomdlg32 -ladvapi32
Also it gives some warnings:
Warning: resolving _my_fucntion#8 by linking to _my_function
Use --enable-stdcall-fixup to disable these warnings
Use --disable-stdcall-fixup to disable these fixups
And this is what qmake says:
g++ -enable-stdcall-fixup -Wl,-enable-auto-import -Wl,-enable-runtime-pseudo-reloc -mthreads -Wl -o debug/aap1.exe debug/main.o -L'c:/Qt/2010.02.1/qt/lib' -lmingw32 -lqtmaind -Lmy_dll.dll -lQtXmld4 -lQtGuid4 -lQtCored4
How can I build my project using qmake?