Protobuf: restore previous output directory

The protobuf upstream implementation has a different default output
directory.  Restore our original output directory for compatibility.

Modules/FindProtobuf.cmake

@@ -210,7 +210,7 @@ function(protobuf_generate)
 
     set(_generated_srcs)
     foreach(_ext ${protobuf_generate_GENERATE_EXTENSIONS})
-      list(APPEND _generated_srcs "${protobuf_generate_PROTOC_OUT_DIR}/${_rel_dir}/${_basename}${_ext}")
+      list(APPEND _generated_srcs "${protobuf_generate_PROTOC_OUT_DIR}/${_basename}${_ext}")
     endforeach()
 
     if(protobuf_generate_DESCRIPTORS AND protobuf_generate_LANGUAGE STREQUAL cpp)
@@ -223,7 +223,7 @@ function(protobuf_generate)
     add_custom_command(
       OUTPUT ${_generated_srcs}
       COMMAND  protobuf::protoc
-      ARGS --${protobuf_generate_LANGUAGE}_out ${_dll_export_decl}${protobuf_generate_PROTOC_OUT_DIR}/${_rel_dir} ${_dll_desc_out} ${_protobuf_include_path} ${_abs_file}
+      ARGS --${protobuf_generate_LANGUAGE}_out ${_dll_export_decl}${protobuf_generate_PROTOC_OUT_DIR} ${_dll_desc_out} ${_protobuf_include_path} ${_abs_file}
       DEPENDS ${_abs_file} protobuf::protoc
       COMMENT "Running ${protobuf_generate_LANGUAGE} protocol buffer compiler on ${_proto}"
       VERBATIM )