bug#45557: 27.1; Incorrect rendering of COMBINING OVERLINE

[Eli Zaretskii]

> From: Stephen Eglen <sje30@cam.ac.uk>
> Date: Wed, 30 Dec 2020 13:42:40 +0000
> 
> emacs -Q
> 
> (set-face-attribute 'default nil :font "JuliaMono")
> 
> (insert 611 773 32 120 773)
> 
> ɣ̅ x̅
> 
> should generate a gamma and x, both with overline.
> 
> gamma is overlined, but not x.

If you move the cursor to x̅, does Emacs display a single cursor block
that includes both x and the overline, or does it behave as if those
were 2 separate glyphs?  If the latter, what does Emacs show in the
*Help* buffer if you go to the ̅ glyph and type "C-u C-x ="?