Add new header apisetcconv.h and added its use to headers


git-svn-id: https://mingw-w64.svn.sourceforge.net/svnroot/mingw-w64@5862 4407c894-4637-0410-b4f5-ada5f102cad1
Add experimental support for apiset.h definitions, prototype, and types.


git-svn-id: https://mingw-w64.svn.sourceforge.net/svnroot/mingw-w64@5863 4407c894-4637-0410-b4f5-ada5f102cad1