No X11. My approach was as follows: I started with the 'Makefile.win32gcc', added compiler and linker flags from 'Makefile.win32', and changed this and that (what seemed to be reasonable in my eyes). Then I excluded the check for X11 from the 'configure' script. After that I changed the included modules in the main 'Makefile'. I had the choice between 'architectures' (again my question: what is the difference between the terms 'architecture' and 'platform'?) 'win32', 'win32gcc' and unix. 'win32' includes the modules 'winnt' and 'win32gdk' (so this is not for native win32 api!?) which made sense to me, so I chose it but renamed it to 'win32gcc'. Later I found that module 'win32gdk' did not build (I got hundreds of warnings, even errors) so I exluded it from the build. As I understand it, this means there is no graphic interface now. Do I have to include module 'win32', which looks like the native win32 interface, instead? But anyway, this doesn't bother me much as my goal is to build a cross-platform graphic interface with FLTK similiar to Qt. In fact, some of this is already working...
As said I've included 'winnt'. Is there anything else besides 'win32'?
Yes, that is what I'm trying to do (except for my FLTK plans, but that is independent from the native win32 interface.) The 'Makefile.win32gcc' still has PLATFORM=linux. If I remember correctly, trying to change this into 'win32' broke the build because win32 has totally different compile and linker scripts - /build/unix vs. /build/win.
As mentioned in the step by step description above, you can get all my modifications from andreas-schoemann.de/root-mingw