bug#42383: 28.0.50; Two bugs with M-x compile

[Stefan Monnier]

>> Upon further investigation, this bug has been introduced by the patch for 
>> bug#34330, which moved pcomplete-completions-at-point last in 
>> shell-dynamic-complete-functions in shell.el:
> Stefan, Alex: any ideas for how to fix this?

I haven't had time to look into this, but I'll just note that the
commit's message says:

    commit e4d17d8cb479ffeeb7dfb7320a1432722ac8df75
    Author: Alex Branham <alex.branham@gmail.com>
    Date:   Thu Aug 15 11:02:38 2019 -0500
    
        Fix filename completion in shell mode buffers
        
        * lisp/shell.el (shell-dynamic-complete-functions): Move
        pcomplete-completions-at-point down the list so that filename
        completion has a chance to complete before pcompletion.
        
        Fixes bug#34330

yet, `pcomplete-completions-at-point` is supposed to perform filename
completion also (via `pcomplete-default-completion-function`), so
I think `pcomplete-completions-at-point` should come first and I suspect
that the problem in bug#34330 is internal to pcomplete and the above
commit just worked around it.


        Stefan