Using an unsophisticated method of going back in time and building various versions of Emacs on the w32 platform, I tracked down the inability to add a few new buffer-local variables in buffer.c/buffer.h to a commit that occurred on 01/31/2019:  05d2fc7170fb66a87601b1c76ddae2c1b7b4b934.

Steps to reproduce the issue:

1.  git reset --hard 05d2fc7170fb66a87601b1c76ddae2c1b7b4b934

2.  Apply the attached patch that adds a few new buffer local variables.

3.  Build a w32 version of Emacs [I use MinGW_32 and ezwinports downloaded a couple of years ago, on a Windows XP SP-3 box]:

CFLAGS='-O0 -g3' ./configure \
--prefix=/c/docume~1/admini~1/desktop/trunk \
--enable-checking='yes,glyphs' \
--enable-check-lisp-object-type \
--without-compress-install \
--without-makeinfo \
--with-gnutls=no \
--with-mailutils \
--without-makeinfo

4.  The build terminates abnormally at the following location:

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]: *** [emacs-lisp/macroexp.elc] Error 3
make[2]: Leaving directory `/c/docume~1/admini~1/desktop/.0.2019_01_31__05d2fc7170fb66a87601b1c76ddae2c1b7b4b934/lisp'
make[1]: *** [bootstrap-emacs.pdmp] Error 2
make[1]: Leaving directory `/c/docume~1/admini~1/desktop/.0.2019_01_31__05d2fc7170fb66a87601b1c76ddae2c1b7b4b934/src'
make: *** [src] Error 2

Beyond pinpointing the exact commit where the Emacs build goes awry, I would be pleased to help further towards resolving this issue -- however, some pointers would be greatly appreciated.  Perhaps there is something that may stand out (to a trained programmer) in the 01/31/2019 commit ....

Keith