I spoke too soon yesterday! I still have problems building on windows.
It seems that if I link with 32bit libsndfile, and rename
libsndfile-1.dll to libsndfile.dll I can build without problems but I
can't run Csound. I get the same problem as before. Trying to build
with 64bit libsndfile gives me the following build error:

C:\Users\Rory\Documents\SourceCode\libsndfile\bin/libsndfile.dll: file
not recognized: File format not recognized
collect2: ld returned 1 exit status
scons: *** [ampmidid.dll] Error 1
scons: building terminated because of errors.

In summary, I can build by linking to 32bit libsndfile, but it won't
run. O the other hand I can't build with 64bit because it says the
library is the wrong format.

So I download and installed Csound for windows, and removed all
references to my own build. I was then able to build a MS lib file
from Mike's csound64.dll.5.2.dll. Now I can build Cabbage, but if I
run it through the MSVC bebugger I get the same errors as before. If I
run the exe on its own it runs fine, although it crashes on exit. I
thought it might have something to do with the platform setting in my
visual studio settings but I double checked that and it's set to
Win32. Any further suggestions? I'm running out of ideas.