[doc]: conditionally include ocaml_doc in ALL target based on LLVM_BUILD_DOCS

Make `ocaml_doc` an ALL target only when `LLVM_BUILD_DOCS` is enabled to avoid unnecessary build steps when documentation generation is not required.

Author: Acture

llvm/docs/CMakeLists.txt

@@ -136,7 +136,12 @@ if( NOT uses_ocaml LESS 0 AND LLVM_ENABLE_OCAMLDOC )
     list(APPEND odoc_files -load ${odoc_file})
   endforeach()
 
-  add_custom_target(ocaml_doc ALL
+  set(OCAML_DOC_ADD_TO_ALL "")
+  if(LLVM_BUILD_DOCS)
+    set(OCAML_DOC_ADD_TO_ALL ALL)
+  endif()
+
+  add_custom_target(ocaml_doc ${OCAML_DOC_ADD_TO_ALL}
     COMMAND ${CMAKE_COMMAND} -E remove_directory ${CMAKE_CURRENT_BINARY_DIR}/ocamldoc/html
     COMMAND ${CMAKE_COMMAND} -E make_directory ${CMAKE_CURRENT_BINARY_DIR}/ocamldoc/html
     COMMAND ${OCAMLFIND} ocamldoc -d ${CMAKE_CURRENT_BINARY_DIR}/ocamldoc/html