>>>> I'm compiling Emacs master right now (on macOS Catalina) and have 
>>>> detected a couple of warnings 'assignment to free variable 
>>>> repeat-map' (one in tab-bar.el and one in window.el) Which I haven't 
>>>> seen before...
>>>
>>> I don't see any warnings, so please show the warnings you see.
>>
>> I see them (and have seen them for a week or two), too:
>>
>> In toplevel form:
>> tab-bar.el:2093:33: Warning: assignment to free variable ‘repeat-map’
>> In toplevel form:
>> window.el:10261:33: Warning: assignment to free variable ‘repeat-map’
>
> Isn't this just the usual case of a stale lisp/ldefs-boot.el?  IOW, I'd 
> expect the warnings to go away when that file is updated to include the 
> repeat-map autoload.
>

I don't know, but I don't think that's the cause.  What I do know is that 
these warnings are displayed when running "make -j" on a fresh clone of 
the repository.