[ ... SNIP ...]

> I have no idea what's going on there. What version of Emacs is that?
> The compilation switches passed to GCC are nowhere near what I'd
> expect given the value of LOCAL_FLAGS in lib-src/makefile.w32-in.

I have reloaded a full trunk branch, and the problem is gone, seems that somehow something was corrupted in my tree.

> > I am now starting to wonder whether all my troubles aren't coming from this that I may have mistakenly some components of my supposedly MingW32 toolchain patched to build for MSYS, rather than to use MSYS. How can one detect that?...
> Look inside the .exe with some dependency checker; if you see a
> dependency on MSYS-1.0.DLL, it's an MSYS executable.

Thanks, I have downloaded dependency walker.

Very best regards and many thanks for all the help and teaching me about MSYS and EMACS building way for MSWindows.