Fix cleanup of existing documentation of target lwipdocs

src/Filelists.cmake

@@ -258,16 +258,11 @@ if (DOXYGEN_FOUND)
     message("Doxygen build started")
 
     add_custom_target(lwipdocs
+        COMMAND ${CMAKE_COMMAND} -E remove_directory ${DOXYGEN_DIR}/${DOXYGEN_OUTPUT_DIR}/html
         COMMAND ${DOXYGEN_EXECUTABLE} ${DOXYGEN_OUT}
         WORKING_DIRECTORY ${DOXYGEN_DIR}
         COMMENT "Generating API documentation with Doxygen"
         VERBATIM)
-
-    # Remove old docs before generating new ones to prevent stale files
-    add_custom_command(TARGET lwipdocs
-        PRE_BUILD
-        COMMAND ${CMAKE_COMMAND} -E remove_directory ${DOXYGEN_DIR}/${DOXYGEN_OUTPUT_DIR}/html
-)
 else (DOXYGEN_FOUND)
     message("Doxygen needs to be installed to generate the doxygen documentation")
 endif (DOXYGEN_FOUND)