bug#26742: Display bug with composed strings

[Eli Zaretskii <eliz@gnu.org>]

> From: Andreas Schwab <schwab@linux-m68k.org>
> Cc: Clément Pit--Claudel <clement.pitclaudel@live.com>,
>   26742@debbugs.gnu.org
> Date: Tue, 02 May 2017 19:18:22 +0200
> 
> I see the same effect, if I use Droid Sans Mono as the default font, but
> not with DejaVu Sans Mono (in the latter case both characters are
> selected from this font).
> 
> The component character(s) are displayed by these fonts (glyph codes):
>  ℝ: xft:-unknown-Linux Libertine O-normal-normal-normal-*-15-*-*-*-*-0-iso10646-1 (#x748)
>  ≤: xft:-unknown-Droid Sans Mono-normal-normal-normal-*-15-*-*-*-m-0-iso10646-1 (#x231)

Aha, so this is somehow font-depended after all.  Thanks.

For the record, on my system, the problem doesn't happen even if the
two characters are displayed using different fonts:

  The component character(s) are displayed by these fonts (glyph codes):
   ℝ: uniscribe:-outline-Symbola-normal-normal-normal-serif-13-*-*-*-p-*-iso10646-1 (#x471)
   ≤: uniscribe:-outline-Courier New-normal-normal-normal-mono-13-*-*-*-c-*-iso8859-1 (#x94)

Does anything change if you add

  --eval "(setq use-default-font-for-symbols nil)"

to the Emacs command line, before the file name to visit?  In my case,
this still doesn't reproduce the problem, and the two characters still
use 2 different fonts, although ≤ now uses a different font, not the
one used by the default face.