Therefore I disabled the MACOSX_DEPLOYMENT_TARGET=10.3 macro. Not sure what negative impact this has. People with MacOSX experience, please look into it (I merely tested it on my Leopard MacBook).
We're still building on 10.4 and 10.5 in various combinations of PPC32, x86 and x86_64 and I'd be concerned this change leads to regressions. If you look in src/configure.in you'll see why MACOSX_DEPLOYMENT_TARGET was introduced in the first place:
# 10.3 or newer take advantage of two-level namespaces to avoid # symbol collisions for e.g. libjpeg which is referenced from both # _Image_JPEG and _Image_TIFF. It requires MACOSX_DEPLOYMENT_TARGET # which is initialized in smartlink to 10.3. LDSHARED="$REALCC $CFLAGS -bundle -bind_at_load -undefined dynamic_lookup"
Have you checked whether those modules still work? Any change if you assign a more recent version number to the environment variable? I don't see a problem with discontinuing support for 10.3 specifically if that helps.