CMake: provide the plugin-related variables insde the project as well.

Until now they were provided only through FindMagnum.cmake.

CMakeLists.txt

@@ -316,5 +316,22 @@ set(MAGNUM_PLUGINS_RELEASE_DIR ${MAGNUM_PLUGINS_RELEASE_DIR_INIT}
 set(MAGNUM_PLUGINS_DIR ${MAGNUM_PLUGINS_DIR_INIT}
     CACHE STRING "Base directory where to look for Magnum plugins")
 
+# Plugin directories
+set(MAGNUM_PLUGINS_FONT_DIR ${MAGNUM_PLUGINS_DIR}/fonts)
+set(MAGNUM_PLUGINS_FONT_DEBUG_DIR ${MAGNUM_PLUGINS_DEBUG_DIR}/fonts)
+set(MAGNUM_PLUGINS_FONT_RELEASE_DIR ${MAGNUM_PLUGINS_RELEASE_DIR}/fonts)
+set(MAGNUM_PLUGINS_FONTCONVERTER_DIR ${MAGNUM_PLUGINS_DIR}/fontconverters)
+set(MAGNUM_PLUGINS_FONTCONVERTER_DEBUG_DIR ${MAGNUM_PLUGINS_DEBUG_DIR}/fontconverters)
+set(MAGNUM_PLUGINS_FONTCONVERTER_RELEASE_DIR ${MAGNUM_PLUGINS_RELEASE_DIR}/fontconverters)
+set(MAGNUM_PLUGINS_IMAGECONVERTER_DIR ${MAGNUM_PLUGINS_DIR}/imageconverters)
+set(MAGNUM_PLUGINS_IMAGECONVERTER_DEBUG_DIR ${MAGNUM_PLUGINS_DEBUG_DIR}/imageconverters)
+set(MAGNUM_PLUGINS_IMAGECONVERTER_RELEASE_DIR ${MAGNUM_PLUGINS_RELEASE_DIR}/imageconverters)
+set(MAGNUM_PLUGINS_IMPORTER_DIR ${MAGNUM_PLUGINS_DIR}/importers)
+set(MAGNUM_PLUGINS_IMPORTER_DEBUG_DIR ${MAGNUM_PLUGINS_DEBUG_DIR}/importers)
+set(MAGNUM_PLUGINS_IMPORTER_RELEASE_DIR ${MAGNUM_PLUGINS_RELEASE_DIR}/importers)
+set(MAGNUM_PLUGINS_AUDIOIMPORTER_DIR ${MAGNUM_PLUGINS_DIR}/audioimporters)
+set(MAGNUM_PLUGINS_AUDIOIMPORTER_DEBUG_DIR ${MAGNUM_PLUGINS_DEBUG_DIR}/audioimporters)
+set(MAGNUM_PLUGINS_AUDIOIMPORTER_RELEASE_DIR ${MAGNUM_PLUGINS_RELEASE_DIR}/audioimporters)
+
 add_subdirectory(modules)
 add_subdirectory(src)