meson.build: always enable Wave encoder for Snapcast

Even if the "wave_encoder" option is disabled (and no other encoder
plugins are enabled), forcefully enable the Wave encoder (if Snapcast
is enabled).

Closes https://github.com/MusicPlayerDaemon/MPD/issues/1500

src/encoder/meson.build

@@ -3,6 +3,22 @@ encoder_features = configuration_data()
 encoder_features.set('ENABLE_ENCODER', need_encoder)
 
 if not need_encoder
+  if need_wave_encoder
+    # Special case for the Snapcast output plugin which only needs the
+    # PCM wave encoder encoder plugin
+    encoder_glue = static_library(
+      'encoder_glue',
+      'plugins/WaveEncoderPlugin.cxx',
+      include_directories: inc,
+    )
+
+    encoder_glue_dep = declare_dependency(
+      link_with: encoder_glue,
+    )
+
+    subdir_done()
+  endif
+
   encoder_glue_dep = dependency('', required: false)
   configure_file(output: 'Features.h', configuration: encoder_features)
   subdir_done()

src/encoder/plugins/meson.build

@@ -35,7 +35,7 @@ if libshine_dep.found()
 endif
 
 encoder_features.set('ENABLE_WAVE_ENCODER', get_option('wave_encoder'))
-if get_option('wave_encoder')
+if get_option('wave_encoder') or need_wave_encoder
   encoder_plugins_sources += 'WaveEncoderPlugin.cxx'
 endif