Fix for cmake 1.11 (#14350)

test=develop

cmake/external/protobuf.cmake

@@ -30,9 +30,7 @@ UNSET_VAR(PROTOBUF_LITE_LIBRARY)
 UNSET_VAR(PROTOBUF_LIBRARY)
 UNSET_VAR(PROTOBUF_INCLUDE_DIR)
 UNSET_VAR(Protobuf_PROTOC_EXECUTABLE)
-
-if(NOT COMMAND protobuf_generate_python)  # before cmake 3.4, protobuf_genrerate_python is not defined.
-    function(protobuf_generate_python SRCS)
+function(protobuf_generate_python SRCS)
     # shameless copy from https://github.com/Kitware/CMake/blob/master/Modules/FindProtobuf.cmake
     if(NOT ARGN)
         message(SEND_ERROR "Error: PROTOBUF_GENERATE_PYTHON() called without any proto files")
@@ -52,7 +50,6 @@ if(NOT COMMAND protobuf_generate_python)  # before cmake 3.4, protobuf_genrerate
     else()
         set(_protobuf_include_path -I ${CMAKE_CURRENT_SOURCE_DIR})
     endif()
-
     if(DEFINED PROTOBUF_IMPORT_DIRS AND NOT DEFINED Protobuf_IMPORT_DIRS)
         set(Protobuf_IMPORT_DIRS "${PROTOBUF_IMPORT_DIRS}")
     endif()
@@ -77,19 +74,17 @@ if(NOT COMMAND protobuf_generate_python)  # before cmake 3.4, protobuf_genrerate
                 set(FIL_WE "${FIL_DIR}/${FIL_WE}")
             endif()
         endif()
-
         list(APPEND ${SRCS} "${CMAKE_CURRENT_BINARY_DIR}/${FIL_WE}_pb2.py")
         add_custom_command(
                 OUTPUT "${CMAKE_CURRENT_BINARY_DIR}/${FIL_WE}_pb2.py"
-                    COMMAND  ${Protobuf_PROTOC_EXECUTABLE} --python_out ${CMAKE_CURRENT_BINARY_DIR} ${_protobuf_include_path} ${ABS_FIL}
-                    DEPENDS ${ABS_FIL} ${Protobuf_PROTOC_EXECUTABLE}
+                COMMAND  ${PROTOBUF_PROTOC_EXECUTABLE} --python_out ${CMAKE_CURRENT_BINARY_DIR} ${_protobuf_include_path} ${ABS_FIL}
+                DEPENDS ${ABS_FIL} ${PROTOBUF_PROTOC_EXECUTABLE}
                 COMMENT "Running Python protocol buffer compiler on ${FIL}"
                 VERBATIM )
     endforeach()
 
     set(${SRCS} ${${SRCS}} PARENT_SCOPE)
-    endfunction()
-endif()
+endfunction()
 
 # Print and set the protobuf library information,
 # finish this cmake process and exit from this file.
@@ -126,6 +121,7 @@ macro(PROMPT_PROTOBUF_LIB)
     # FIND_Protobuf.cmake uses `Protobuf_PROTOC_EXECUTABLE`.
     # make `protobuf_generate_cpp` happy.
     SET(Protobuf_PROTOC_EXECUTABLE ${PROTOBUF_PROTOC_EXECUTABLE})
+
     FOREACH(dep ${protobuf_DEPS})
         ADD_DEPENDENCIES(protobuf ${dep})
         ADD_DEPENDENCIES(protobuf_lite ${dep})