Some drv files as symbolic links cause make sources problems on Windows

[MarcMazas]

Hi. For information: After cloning the git repo on Windows / Eclipse through EGit, I got the XXXOpenCustomHashMap.drv / XXXOpenCustomHashSet.drv & the like files containing a single line of text OpenHashMap.drv / OpenHashSet.drv. So the make sources command failed to generate the corresponding java files. I had to replace their contents with the target contents.