[SV 41983] Support omitting the text argument to $(file ...)

Reported by Tim Murphy <tnmurphy@gmail.com>
* function.c (func_file): Only write TEXT if it is not NULL.
* NEWS, doc/make.texi: Document the new feature
* tests/scripts/functions/file: Verify that the no-text version of
  $(file ...) works and doesn't add a newline.
4 files changed