In my original patch, I placed the added Build-Dependency naïvely next
to libmodplug instead of alphabetically.
I made sure to test build this fixed patch from a clean unstable VM, and
the resulting package has the OpenMPT plugin included.
Here is the fixed patch:
--- a/debian/control 2020-04-07 14:29:22.000000000 -0400
+++ b/debian/control 2020-04-07 14:30:25.090277399 -0400
@@ -35,6 +35,7 @@
libneon27-gnutls-dev (>= 0.26),
libnotify-dev,
libogg-dev (>= 1.0),
+ libopenmpt-dev (>= 0.2),
libpulse-dev (>= 0.9) [linux-any],
libsamplerate0-dev (>= 0.0.15),
libsdl2-dev,
