NT mingw/msys build problem

[Guy Gascoigne-Piggford <guy@wyrdrune.com>]

I've been trying to track down a problem that my NT build has when 
building with the latest mingw+msys environment.  Emacs builds and runs, 
but certain autoloads seem to be missing, after much hunting through 
build logs I ended out with this being the cause of the problem:

Eventually make runs this:

"./../bin/emacs.exe" -batch --no-init-file --no-site-file --multibyte -l 
autoload \
    --eval '(setq find-file-hooks nil \
        find-file-suppress-same-file-warnings t \
        generated-autoload-file \
          "c:/dev/emacs-src/emacs/lisp/loaddefs.el")' \
    -f batch-update-autoloads c:/dev/emacs-src/emacs/lisp calc calendar 
emacs-lisp emulation eshell gnus international language mail mh-e net 
obsolete play progmodes term textmodes toolbar url

the output of which is:

Wrote c:/dev/emacs-src/emacs/lisp/c;C:Devmsys.0evacs-srcacslisploaddefs.el
Loading vc-cvs...
Wrote c:/dev/emacs-src/emacs/lisp/c;C:Devmsys.0evacs-srcacslisploaddefs.el
Autoloads file 
c:/dev/emacs-src/emacs/lisp/c;C:Devmsys.0evacs-srcacslisploaddefs.el 
does not exist

I'm explicitly passing files of a style that I'd expect emacs to 
understand, but it looks like some part of the process is switching them 
back to dos style slashes and then passing them back to something that 
expects unix style names.

Anyway I'm a bit stumped as to how to work around this, has anyone else 
seen this or have a suggestion?

Guy