CMake: Link against LibSoftGPU to enable WebGL using serenity LibGL

In the future, ladybird should probably use a QOpenGLWidget or similar
platform plugin to use the native GL implementation instead of the one
in serenity.

CMakeLists.txt

@@ -64,7 +64,7 @@ set(SOURCES
 qt_add_executable(ladybird ${SOURCES}
  MANUAL_FINALIZATION
 )
-target_link_libraries(ladybird PRIVATE Qt::Widgets Qt::Network LibWeb LibWebSocket LibGL LibMain)
+target_link_libraries(ladybird PRIVATE Qt::Widgets Qt::Network LibWeb LibWebSocket LibGL LibSoftGPU LibMain)
 
 set_target_properties(ladybird PROPERTIES
  MACOSX_BUNDLE_GUI_IDENTIFIER org.serenityos.ladybird