These were created as symlinks, which doesn't work with Win32 make as it
doesn't understand Cygwin symlinks.

Instead, create them as actual files.

Note: the reason why they work as symlinks at all is that the Makefile
uses $(realpath) and partial_build.mk does not, so they can
resolve relative paths from 2 different directories...

Change-Id: I4a9abffae82561111a9525fb35ed4b174cc8d96a
Reviewed-on: https://gerrit.libreoffice.org/56691
Tested-by: Jenkins
Reviewed-by: Thorsten Behrens <Thorsten.Behrens@CIB.de>