Improve handling of import code from library

On Windows:
- Items starting with -l are ignored
- Everything else is treated as an ASCII library file

On other platforms:
- Items starting with -l are treated as shared libraries
- Items containing a dot are treated as normal files and linked
- Other items are ignored

This allows one to use for example:

	import code from library "mylib_library"
	import code from library "-lmylib"

(where Clean System Files\mylib_library refers to mylib.dll or so).
The first entry is used on Windows; the second on non-Windows.
1 job for fix-shared-libraries-for-windows in 1 minute and 20 seconds (queued for 1 second)