Move Windows replacement functions to enterprise.

Move the actual files and make sure detection is done properly and in
the right place.
Enable builtin extensions by default on Windows.

Loading them dynamically is not supported there.
Keep build flags in separate variables for configure tests to work.

They are needed for the actual build, but not during configure tests,
which will fail if they are defined.
Add missing define test for *netgrent functions.
Merge pull request #911 from kacfengine/repo_split_windows

Fixing Windows build after repo split.