>> cp -f temacs.exe bootstrap-emacs.exe
>> rm -f bootstrap-emacs.pdmp
>> ./temacs --batch  -l loadup --temacs=pbootstrap \
>>         --bin-dest /ucrt64/bin/ --eln-dest /ucrt64/lib/emacs/30.0.50/
>> C:\Users\arthu\repos\emsrc\ucrt-02-21\src\temacs.exe: Write error to standard output: No such file or directory
>> make[2]: *** [Makefile:1014: bootstrap-emacs.pdmp] Error 1
>> 
>> Question is which file or directory? Dump file? Bad path? Bad encoding?
>> Something in loadup.el or elsewhere?
>> 
>> If I comment away exit on failure as they do in mingw patch, than everything
>> builds and seemnigly works. However I have experienced one crash where system
>> killed Emacs, similar as those I have seen with the version from gnu ftp
>> (29.2_1).
>> 
>> How do I debug temacs bootstrap?
>
> You run the failing command under GDB, putting a breakpoint on the
> line that emits that error message, and when the breakpoint breaks,
> look around to see what happened and why.  In this case, the ENOENT
> value of errno is peculiar, since stdout is not redirected to any
> file, AFAIU, so why does close_stream report ENOENT?  One possible
> reason is that close_stream should zero out errno before it starts its
> processing, to avoid reporting a stale value of errno from some
> unrelated call.