#746 GDI+ & Direct2D/DirectWrite support for OpenWatcom

[Bastian Märkisch]

Despite the fact that GDI+ shipped already with Windows XP, OpenWatcom still does not support it. The attached file contains include files copied from MSYS2/Mingw64 and adopted slightly to be used with OpenWatcom, and the corresponding library.

The preferred Windows terminal backend for version 5.3 is based on Direct2D & DirectWrite, which are available since Windows 7. Attached to this tracker is a package with include files adopted from Mingw64, and the corresponding libraries.

Although these are not strictly patches to gnuplot, I am putting them here, since they enables us to drop support for the old GDI variant of the windows terminal in the future.