buildsystem - a bit of re-organizing the docs/api CMake

docs/api/CMakeLists.txt

@@ -9,6 +9,25 @@
 # Contact KDAB at <info@kdab.com> for commercial licensing options.
 #
 
+# dot should come with Doxygen find_package(Doxygen)
+if(DOXYGEN_DOT_EXECUTABLE)
+  set(HAVE_DOT "YES")
+else()
+  set(HAVE_DOT "NO")
+  message(STATUS "Unable to provide inheritance diagrams for the API documentation. To fix, install the graphviz project from https://www.graphviz.org")
+endif()
+
+# qhelpgenerator
+find_program(QHELPGEN_EXECUTABLE qhelpgenerator
+  HINTS ${QT_INSTALL_BINS}
+)
+if(QHELPGEN_EXECUTABLE)
+  set(HAVE_QHELPGEN "YES")
+else()
+  set(HAVE_QHELPGEN "NO")
+  message(STATUS "Unable to generate the API documentation in qch format. To fix, install the qthelpgenerator program which comes with Qt.")
+endif()
+
 find_file(QDOC_QTCORE_TAG qtcore.tags
   HINTS ${QT_INSTALL_DOCS}/qtcore
   HINTS ${QT_INSTALL_DATA}/doc/qtcore