Fix a build issue where the python module could become stale.

We are using hardlinks instead of symlinks, and we attempted to
have some logic where we don't re-create the link if the target
file already exists.  This logic is faulty, however, when you
manually delete the source file (e.g. liblldb.dll) and then rebuild
lldb so that a brand new liblldb.dll gets written.  Now the two files
have different inodes, but the target exists, so we would not remake
the link and the target would become stale.

We fix this by only doing the optimization if they are really the
exact same file (by comparing inode numbers), and if they are not
the same file but the target exists, we delete it and re-create
the link.

llvm-svn: 263844