bug#50975: 28.0.60; mh-utils-tests fail with native compilation

[Eli Zaretskii]

> From: Ken Brown <kbrown@cornell.edu>
> Date: Sat, 2 Oct 2021 14:49:04 -0400
> 
> Most of the tests in mh-utils-tests fail if I build the emacs-28 branch on 
> Cygwin with native compilation:
> 
> $ make -C test mh-utils-tests
> make: Entering directory 
> '/home/kbrown/src/emacs/x86_64-emacs-28-native-lisp/test'
> make[1]: Entering directory 
> '/home/kbrown/src/emacs/x86_64-emacs-28-native-lisp/test'
>    GEN      lisp/mh-e/mh-utils-tests.log
> Running 16 tests (2021-10-02 14:13:13-0400, selector ‘(not (tag :unstable))’)
> No MH variant found on the system
> call-process mock unexpected arglist (emacs --batch -l 
> /tmp/emacs-int-comp-subr--trampoline-66696c652d6469726563746f72792d70_file_directory_p_0-rg5Ucy.el)
> call-process mock unexpected arglist (emacs --batch -l 
> /tmp/emacs-int-comp-subr--trampoline-66696c652d6469726563746f72792d70_file_directory_p_0-f6P2ZU.el)
> Test mh-folder-completion-function-02-empty backtrace:

Andrea, please look into this when you have time.

Thanks.