Remove warning in autotools and make LOVE_OLD_MODPLUG define that disables some new modplug settings

platform/unix/gen-makefile

@@ -6,7 +6,6 @@ inc_modules="$inc_current/modules"
 inc_libraries="$inc_current/libraries"
 echo "AM_CPPFLAGS = -I$inc_current -I$inc_modules -I$inc_libraries -I/usr/include/AL -I/usr/include/freetype2  \$(INCLUDE_LUA) -I/usr/include/SDL \$(FILE_OFFSET)
 AUTOMAKE_OPTIONS = subdir-objects
-DEFAULT_INCLUDES =
 SUBDIRS =
 
 # LÖVE executable

src/modules/sound/lullaby/ModPlugDecoder.cpp

@@ -42,8 +42,12 @@ namespace lullaby
 		// fill with modplug defaults (modplug _memsets_, so we could get
 		// garbage settings when the struct is only partially initialized)
 		// This does not exist yet on Windows.
+
+		// Some settings not supported by some older versions
+#ifndef LOVE_OLD_MODPLUG
 		settings.mStereoSeparation = 128;
 		settings.mMaxMixChannels = 32;
+#endif
 		settings.mReverbDepth = 0;
 		settings.mReverbDelay = 0;
 		settings.mBassAmount = 0;