make-docfile warnings

[Po Lu]

I get these trying to build make-docfile:

make-docfile.c: In function ‘scan_lisp_file’:
make-docfile.c:1333:7: warning: unused variable ‘flen’ [-Wunused-variable]
 1333 |   int flen = strlen (filename);
      |       ^~~~
make-docfile.c:1332:7: warning: unused variable ‘i’ [-Wunused-variable]
 1332 |   int i;

Someone should fix that, thanks.