Windows incremental build is broken with JDK-8217728

In JDK-8217728 the incremental build was speed up, using concatenated dependency files. The problem is, that on Windows these dependency files are generated via a script, which lets all lines end with a backslash. This is OK for a single dependency, but if these are just concatenated in a single file, it now looks like one big line.

One way to fix this, is to add an empty line at the end of the windows deps files.