sdkddkver.h: Updated for Win8, IE9 and IE10.

git-svn-id: https://svn.code.sf.net/p/mingw-w64/code@6531 4407c894-4637-0410-b4f5-ada5f102cad1
_mingw.h: Don't define WINVER here, leave it up to sdkddkver.h (or a few other places).

git-svn-id: https://svn.code.sf.net/p/mingw-w64/code@6532 4407c894-4637-0410-b4f5-ada5f102cad1
Makefile.am: Define _WIN32_WINNT globally in CFLAGS.

git-svn-id: https://svn.code.sf.net/p/mingw-w64/code@6533 4407c894-4637-0410-b4f5-ada5f102cad1