How to set the QT_DLL macro?

[Angus Leeming]

This is partly a report that I've successfully built LyX 1.3.x for Windows
using the mingw cross-compiler on linux, but it's also a request for help. 

In order for the linking to succeed, I have to define the QT_DLL macro when
building LyX's Qt code.. If I don't then linking fails with vast numbers
of warnings like:

frontends/.libs/libfrontends.a(QBibitemDialogBase.o)(.text+0x583): In
function `_ZNK6QGList5countEv':
/home/angus/lyx/13x/build-mingw-xcompile/src/frontends/qt2/ui/QBibitemDialogBase.C:
variable 'vtable for QSpacerItem' can't be auto-imported. Please read the
documentation for ld's --enable-auto-import for details.

I'm currently passing -DQT_DLL to the compiler explicitly. However, I don't
need to do that when compiling using the mingw compiler natively on
Windows, so suspect that there's another way. What is the 'correct' way to
specify the QT_DLL macro?

Any clues?

Regards,
Angus

ps, linking against the qt3.dll is still excrutiatingly slow. Compilation
is far quicker, but the final link still takes ~20 minutes :(

pps, I may have compiled lyx, but trying to start it up on Windows results
in an error dialog "The application failed to initialise itself
correctly" :(