Fixed protobuf_generate output definition for files relative to the protobuf_generate command

cmake/protobuf-config.cmake.in

@@ -92,11 +92,13 @@ function(protobuf_generate)
   set(_generated_srcs_all)
   foreach(_proto ${protobuf_generate_PROTOS})
     get_filename_component(_abs_file ${_proto} ABSOLUTE)
+    get_filename_component(_abs_dir ${_abs_file} DIRECTORY)
     get_filename_component(_basename ${_proto} NAME_WE)
+    file(RELATIVE_PATH _rel_dir ${CMAKE_CURRENT_SOURCE_DIR} ${_abs_dir})
 
     set(_generated_srcs)
     foreach(_ext ${protobuf_generate_GENERATE_EXTENSIONS})
-      list(APPEND _generated_srcs "${protobuf_generate_PROTOC_OUT_DIR}/${_basename}${_ext}")
+      list(APPEND _generated_srcs "${protobuf_generate_PROTOC_OUT_DIR}/${_rel_dir}/${_basename}${_ext}")
     endforeach()
     list(APPEND _generated_srcs_all ${_generated_srcs})