output/jack: enable on Windows

This enables the JACK output plugin on Windows, but doesn't link
against libjack64.dll, instead loads the DLL at runtime with
LoadLibrary().  This kludge avoids the extremely fragile JACK shared
memory protocol by using the system's libjack64.dll, without requiring
the same DLL at build time.

win32/build.py

@@ -108,6 +108,7 @@ thirdparty_libs = [
     curl,
     libexpat,
     libnfs,
+    jack,
     boost,
 ]