apple: build static library

Move build rules from src/output/plugins/meson.build

src/apple/meson.build

@@ -0,0 +1,27 @@
+if not is_darwin
+  apple_dep = dependency('', required: false)
+  subdir_done()
+endif
+
+audiounit_dep = declare_dependency(
+  link_args: ['-framework', 'AudioUnit', '-framework', 'CoreAudio', '-framework', 'CoreServices'],
+  dependencies: [
+    boost_dep,
+  ],
+)
+
+apple = static_library(
+  'apple',
+  'Throw.cxx',
+  include_directories: inc,
+  dependencies: [
+    audiounit_dep,
+  ],
+)
+
+apple_dep = declare_dependency(
+  link_with: apple,
+  dependencies: [
+    audiounit_dep,
+  ],
+)