Make sure targets depending on tomahawklib also include LIBATTICA_INCLUDE_DIR.

If x11-toolkits/attica is not installed in a location such as
${LOCALBASE}/include, we risk breaking the build like this:

  In file included from /wrkdirs/usr/ports/audio/tomahawk/work/tomahawk-0.8.4/src/infoplugins/generic/charts/ChartsPlugin.cpp:29:
  In file included from /wrkdirs/usr/ports/audio/tomahawk/work/tomahawk-0.8.4/src/libtomahawk/TomahawkSettings.h:28:
  /wrkdirs/usr/ports/audio/tomahawk/work/tomahawk-0.8.4/src/libtomahawk/AtticaManager.h:30:10: fatal error: 'attica/provider.h' file not found
  #include <attica/provider.h>
--- src/libtomahawk/CMakeLists.txt.orig	2015-04-15 04:41:40 UTC
+++ src/libtomahawk/CMakeLists.txt
@@ -488,6 +488,9 @@ set_target_properties(
             OUTPUT_NAME "tomahawk"
 )
 
+if(LIBATTICA_FOUND)
+    TARGET_INCLUDE_DIRECTORIES(tomahawklib INTERFACE ${LIBATTICA_INCLUDE_DIR})
+endif(LIBATTICA_FOUND)
 
 qt5_use_modules(tomahawklib Widgets Network Sql WebKitWidgets Concurrent Xml UiTools Svg)