ShaderTools: recognize also the Kernel stage.

src/Magnum/ShaderTools/Stage.cpp

@@ -50,6 +50,7 @@ Debug& operator<<(Debug& debug, const Stage value) {
         _c(RayCallable)
         _c(MeshTask)
         _c(Mesh)
+        _c(Kernel)
         #undef _c
         /* LCOV_EXCL_STOP */
     }

src/Magnum/ShaderTools/Stage.h

@@ -75,7 +75,15 @@ enum class Stage: UnsignedInt {
     RayCallable,                /**< Ray callable stage */
 
     MeshTask,                   /**< Mesh task stage */
-    Mesh                        /**< Mesh stage */
+    Mesh,                       /**< Mesh stage */
+
+    /**
+     * Compute kernel.
+     *
+     * Compared to @ref Stage::Compute, which is used by graphics APIs such as
+     * Vulkan or OpenGL, this one is for use by OpenCL.
+     */
+    Kernel
 };
 
 /**