deps: create empty file instead of dummy file. This change is per an automake thread, see both before and after: https://lists.gnu.org/archive/html/automake/2022-05/msg00006.html * lib/am/depend.am ($(am__depfiles_remade)): create empty files for dependencies instead of files with a line '# dummy'. Turns out this is noticeably faster. * THANKS: update Jan's email address. * NEWS: mention this.