bug#25951: [PATCH] Fix quoted files for 'verify-visited-file-modtime'

[npostavs]

Glenn Morris <rgm@gnu.org> writes:

> This fails to build: http://hydra.nixos.org/build/52549555

    Loading 
/tmp/nix-build-emacs-tarball-unknown.drv-0/x1vxdahi72zl4bj2yd676ichh4iwi9iw-git-export/lisp/files.el
 (source)...
    Warning: Unknown defun property `gv-setter' in cl-fifth
    Warning: Unknown defun property `gv-setter' in cl-sixth
    Warning: Unknown defun property `gv-setter' in cl-seventh
    Warning: Unknown defun property `gv-setter' in cl-eighth
    Warning: Unknown defun property `gv-setter' in cl-ninth
    Warning: Unknown defun property `gv-setter' in cl-tenth
    Symbol's function definition is void: gv-define-simple-setter
    make[1]: *** [bootstrap-emacs] Error 255

Looks like my suggestion of using cl-letf doesn't work because it's too
early in the bootstrap process.  Should work with the original code (but
perhaps add a comment about why we can't use cl-letf).