cmake: build cairo lib and example UI by default if possible

Signed-off-by: falkTX <falktx@falktx.com>

CMakeLists.txt

@@ -29,15 +29,23 @@ list(APPEND CMAKE_MODULE_PATH "${PROJECT_SOURCE_DIR}/cmake")
 include(DPF-plugin)
 
 if(DPF_LIBRARIES)
-  if(NOT (WIN32 OR APPLE)) # TODO skip this one for now
-    dpf__add_dgl_cairo(FALSE)
+  find_package(PkgConfig)
+  if(PKG_CONFIG_FOUND)
+    pkg_check_modules(CAIRO "cairo")
+    if(CAIRO_FOUND)
+      dpf__add_dgl_cairo(FALSE)
+    endif()
   endif()
   dpf__add_dgl_opengl(FALSE)
 endif()
 
 if(DPF_EXAMPLES)
-  if(NOT (WIN32 OR APPLE)) # TODO skip this one for now
-    add_subdirectory("examples/CairoUI")
+  find_package(PkgConfig)
+  if(PKG_CONFIG_FOUND)
+    pkg_check_modules(CAIRO "cairo")
+    if(CAIRO_FOUND)
+      add_subdirectory("examples/CairoUI")
+    endif()
   endif()
   #add_subdirectory("examples/ExternalUI")
   add_subdirectory("examples/FileHandling")