Bug 436037

I try to build Plasma using kdesrc-build tool, under KDE Neon, but fails:

```
-- The following REQUIRED packages have been found:

 * Qt5Gui (required version >= 5.15.2)
 * Qt5WaylandClient
 * Qt5Network (required version >= 5.15.2)
 * Qt5Qml
 * Qt5 (required version >= 5.15.0)
 * Threads
 * Qt5XkbCommonSupport
 * ECM (required version >= 5.78)
 * Qt5Core
 * Wayland (required version >= 1.3), C library implementation of the Wayland protocol: a protocol for a compositor to talk to its clients, <https://wayland.freedesktop.org/>
 * PkgConfig
 * WaylandScanner, Executable that converts XML protocol files to C code, <https://wayland.freedesktop.org/>

-- Configuring done
CMake Error at src/CMakeLists.txt:29 (add_library):
  Target "layer-shell" links to target "Qt::WaylandClientPrivate" but the
  target was not found.  Perhaps a find_package() call is missing for an
  IMPORTED target, or an ALIAS target is missing?


CMake Error at src/CMakeLists.txt:18 (add_library):
  Target "LayerShellQtInterface" links to target "Qt::WaylandClientPrivate"
  but the target was not found.  Perhaps a find_package() call is missing for
  an IMPORTED target, or an ALIAS target is missing?


CMake Error at src/CMakeLists.txt:18 (add_library):
  Target "LayerShellQtInterface" links to target "Qt::WaylandClientPrivate"
  but the target was not found.  Perhaps a find_package() call is missing for
  an IMPORTED target, or an ALIAS target is missing?


-- Generating done
CMake Generate step failed.  Build files cannot be regenerated correctly.
```

What am I missing?