CMake: Link necessary libraries for hosting plugins

The CoreAudioKit (and on macOS, AudioUnit) frameworks are required to
host AudioUnit plugins. Hosts (especially those which don't use the
`juce_audio_utils` module) should use the new `PLUGINHOST_AU` parameter
to `juce_add_*` in order to add the correct preprocessor definition and
link the necessary frameworks.

examples/CMake/readme.md

@@ -399,6 +399,12 @@ attributes directly to these creation functions, rather than adding them later.
     `AAX_ePlugInCategory_SWGenerators`, `AAX_ePlugInCategory_WrappedPlugin`,
     `AAX_ePlugInCategory_Effect`
 
+- `PLUGINHOST_AU`
+  - May be either TRUE or FALSE (defaults to FALSE). If TRUE, will add the preprocessor definition
+    `JUCE_PLUGINHOST_AU=1` to the new target, and will link the macOS frameworks necessary for
+    hosting plugins. Using this parameter should be preferred over using
+    `target_compile_definitions` to manually set the `JUCE_PLUGINHOST_AU` preprocessor definition.
+
 - `COPY_PLUGIN_AFTER_BUILD`
   - Whether or not to install the plugin to the current system after building. False by default.
     If you want all of the plugins in a subdirectory to be installed automatically after building,

extras/AudioPluginHost/CMakeLists.txt

@@ -17,7 +17,8 @@
 juce_add_gui_app(AudioPluginHost
     BUNDLE_ID                       com.juce.pluginhost
     ICON_BIG                        "${CMAKE_CURRENT_SOURCE_DIR}/Source/JUCEAppIcon.png"
-    MICROPHONE_PERMISSION_ENABLED   TRUE)
+    MICROPHONE_PERMISSION_ENABLED   TRUE
+    PLUGINHOST_AU                   TRUE)
 
 juce_generate_juce_header(AudioPluginHost)
 
@@ -33,7 +34,6 @@ target_compile_definitions(AudioPluginHost PRIVATE
     PIP_JUCE_EXAMPLES_DIRECTORY_STRING="${JUCE_SOURCE_DIR}/examples"
     JUCE_ALSA=1
     JUCE_DIRECTSOUND=1
-    JUCE_PLUGINHOST_AU=1
     JUCE_PLUGINHOST_LADSPA=1
     JUCE_PLUGINHOST_VST=0
     JUCE_PLUGINHOST_VST3=1

extras/Build/CMake/JUCEUtils.cmake

@@ -1634,6 +1634,8 @@ function(_juce_set_fallback_properties target)
     _juce_set_property_if_not_set(${target} DISABLE_AAX_BYPASS FALSE)
     _juce_set_property_if_not_set(${target} DISABLE_AAX_MULTI_MONO FALSE)
 
+    _juce_set_property_if_not_set(${target} PLUGINHOST_AU FALSE)
+
     get_target_property(bundle_id ${target} JUCE_BUNDLE_ID)
     _juce_set_property_if_not_set(${target} AAX_IDENTIFIER ${bundle_id})
 
@@ -1824,6 +1826,7 @@ function(_juce_initialise_target target)
         AU_EXPORT_PREFIX
         AU_SANDBOX_SAFE
         AAX_CATEGORY
+        PLUGINHOST_AU                   # Set this true if you want to host AU plugins
 
         VST_COPY_DIR
         VST3_COPY_DIR
@@ -1894,6 +1897,22 @@ function(_juce_initialise_target target)
         $<TARGET_PROPERTY:${target},JUCE_GENERATED_SOURCES_DIRECTORY>)
     target_link_libraries(${target} PUBLIC $<$<TARGET_EXISTS:juce_vst2_sdk>:juce_vst2_sdk>)
 
+    get_target_property(is_pluginhost_au ${target} JUCE_PLUGINHOST_AU)
+
+    if(is_pluginhost_au)
+        target_compile_definitions(${target} PUBLIC JUCE_PLUGINHOST_AU=1)
+
+        if(CMAKE_SYSTEM_NAME STREQUAL "Darwin" OR CMAKE_SYSTEM_NAME STREQUAL "iOS")
+            find_library(AU_CoreAudioKit CoreAudioKit REQUIRED)
+            target_link_libraries(${target} PRIVATE ${AU_CoreAudioKit})
+        endif()
+
+        if(CMAKE_SYSTEM_NAME STREQUAL "Darwin")
+            find_library(AU_AudioUnit AudioUnit REQUIRED)
+            target_link_libraries(${target} PRIVATE ${AU_AudioUnit})
+        endif()
+    endif()
+
     _juce_write_generate_time_info(${target})
     _juce_link_optional_libraries(${target})
 endfunction()