SL-18289: Modify autobuild.xml to insert a CMaker architecture flag as well as the generator string for Windows builds

Implied 'branch' is now two different version-control systems behind

Part of his change was omly taking Release builds into account, the other
part from me made the same mistake.
Use a generator expression with a custom command to get the symlink the way
we want.

one genex that needed changing.
Interstingly add_custom_target will not complain about a file
that would never be declared as OUTPUT and thus is not really a
valid cmake build target.``