This is no official system DLL and WineD3D is its only user. But latest WineD3D prefers the libtxc_dxtn codebase instead of the alternative library we used.
This is also what Mesa uses and Fedora ships now that the patents have expired, so we should stick to the same.
I'm importing the libtxc_dxtn-1.0.1 codebase from https://people.freedesktop.org/~cbrill/libtxc_dxtn/
It compiles warning-free in our tree without modifying a single line!
I'm merging this Pull Request based on the positive response in CORE-12759.
I lack a proper test case myself, but my version at least shouldn't make things worse. In my opinion, the previous one was broken anyway due to using stdcall imports when WineD3D called cdecl ones.
This also removes the NSWPAT option from our buildsystem as dxtn was its latest user.
