bug#43725: 28.0.50; Include feature/native-comp into master

[Eli Zaretskii]

Andrea, I see in comp.c and comp.el you many times use 'concat'
instead of expand-file-name to construct a file name from the leading
directories and a basename.  Sometimes even a mix of the two.  Here's
one example:

  return Fexpand_file_name (filename,
                            concat2 (Ffile_name_as_directory (base_dir),
                                     Vcomp_native_version_dir));

Is there a reason for using 'concat' in these cases?  E.g., the above
could be written as

  return Fexpand_file_name (filename
                            Fexpand_file_name (Vcomp_native_version_dir,
                                               base_dir));

which also makes only 2 function calls instead of 3.  Am I missing
something?