Just did a little research, its odd that it fails on mixed line endings. Probably a pretection to keep you from setting it for binary files.
SVN diff works it just produces garbage that I have to hand edit each time.
This is with this command.
svn.exe diff --extensions --unified=1 --extensions --ignore-eol-style > filename-unix.patch
The following command what's to remove nearly all the lines and then readd them with new line endings
svn.exe diff > filename-unix2.patch
Tim S