Based on a comment by Florian Weimer in:
https://lists.gnu.org/r/bug-gnulib/2019-06/msg00007.html
It turns out that Emacs (which will use this module) won’t need an
emulation and I suspect other programs won’t either, because these
programs will need to fall back on read+write anyway. Perhaps I
am wrong and other programs will be able to use an emulation; if
so, this patch can be reverted.
* lib/copy-file-range.c (COPY_FILE_RANGE): Replace with a stub.
Just call it copy_file_range.
* m4/copy-file-range.m4 (gl_FUNC_COPY_FILE_RANGE):
Check via AC_LINK_IFELSE.
* modules/copy-file-range (Depends-on): Remove modules no longer used.