w32 master branch: "make[2]: *** [calendar/cal-loaddefs.el] Error 3"

[Keith David Bershatsky]

I am able to successfully build Emacs master branch 03/28/2019 on NS and X11, 
however, the w32 build fails (Windows XP SP-3, using MinGW-32 and the 
ezwinports goodies from a couple of years ago):

This application has requested the Runtime to terminate it in an unusual way.
Please contact the application's support team for more information.
make[2]: *** [calendar/cal-loaddefs.el] Error 3
make[2]: Leaving directory `/c/docume~1/admini~1/desktop/emacs/lisp'
make[1]: *** [../lisp/loaddefs.el] Error 2
make[1]: Leaving directory `/c/docume~1/admini~1/desktop/emacs/src'
make: *** [src] Error 2

[The last time I tried and successfully built the master branch on a w32 
machine was early-mid December 2018, so something has changed in the last 3.5 
months that breaks the build process.]

Q:  How can I assist the Emacs team to debug this issue?