Cleanup doc cmake files (#4473)

doc/CMakeLists.txt

@@ -16,15 +16,15 @@
 
 add_subdirectory(examples)
 
-if ("${NGRAPH_DOC_BUILD_ENABLE}" MATCHES "^ON$")
-    add_custom_target( docs
+if (NGRAPH_DOC_BUILD_ENABLE)
+    add_custom_target(docs
         COMMENT "Build all of the documentation types selected during CMake configuration."
         )
 
-    add_subdirectory( doxygen )
-    add_subdirectory( sphinx )
+    add_subdirectory(doxygen)
+    add_subdirectory(sphinx)
 else()
-    add_custom_target( docs
+    add_custom_target(docs
         COMMAND echo
         COMMAND echo "The 'docs' target is disabled. To enable the building of documentation, re-run cmake with the option -DNGRAPH_DOC_BUILD_ENABLE=ON."
         COMMAND echo

doc/doxygen/CMakeLists.txt

@@ -15,14 +15,16 @@
 # ******************************************************************************
 
 find_package(Doxygen REQUIRED)
+# include(FetchContent)
+# include(${CMAKE_SOURCE_DIR}/cmake/doxygen.cmake)
 
-if ("${NGRAPH_DOXYGEN_WARN_IF_UNDOCUMENTED}" MATCHES "^ON$")
+if (NGRAPH_DOXYGEN_WARN_IF_UNDOCUMENTED)
     set(DOXYGEN_WARN_IF_UNDOCUMENTED YES)
 else()
     set(DOXYGEN_WARN_IF_UNDOCUMENTED NO)
 endif()
 
-if ("${NGRAPH_DOXYGEN_QUIET}" MATCHES "^ON$")
+if (NGRAPH_DOXYGEN_QUIET)
     set(DOXYGEN_QUIET YES)
 else()
     set(DOXYGEN_QUIET NO)
@@ -39,7 +41,7 @@ add_custom_target(doxygen-docs
     COMMENT "Generating documentation with Doxygen"
     VERBATIM )
 
-add_dependencies( docs doxygen-docs )
+add_dependencies(docs doxygen-docs)
 
 install(
     DIRECTORY "${CMAKE_CURRENT_BINARY_DIR}/html/"