People who build the Emacs master branch on MS-Windows should be aware
of changes introduced in commit 8cc8ad0, which switch Emacs to use the
Gnulib 'tempname' and 'mkostemp' functions (for details see the
discussion in bug#28023). If you get warnings or errors during the
build, do "touch configure.ac" and try again. If that doesn't help
either, please report the details here.