configure doesn't handle --with-emacs properly

Running on cygwin under Win 11...

If I run:
    ./configure --with-emacs "/c/MyPrograms/Emacs/emacs-29.1/bin/emacs"
Then the lisp/Makefile sets:
    EMACS_PROG =yes
Rather than the expected:
    EMACS_PRO\GS="/c/MyPrograms/Emacs/emacs-29.1/bin/emacs"

I also get error messages of form:
   configure: WARNING: you should use --build, --host, --target
   configure: WARNING: invalid host type: /c/MyPrograms/Emacs/emacs-29.1/bin/emacs

and:
   checking checking emacs-type of yes... yes: unknown option -- no-site-file
   Try 'yes --help' for more information.

   checking checking emacs-version of yes... yes: unknown option -- no-site-file
   Try 'yes --help' for more information.
   ./configure: line 2500: test: -lt: unary operator expected

   checking otherdirs... yes: unknown option -- no-site-file
   Try 'yes --help' for more information.

So there seems to be something wrong with the parsing/script logic here...