emacs: doesn't display # or ' anymore

[yurkobb]

Describe the bug

Symbols like # (hash) and ' (single quote) are rendered with boxes on screen. The following fragment:

(list '(a b "#hashtag"))

...renders as:

To Reproduce
Steps to reproduce the behavior:

1. nix-shell '<nixos>' -p emacs (or <nixpkgs> - tested both)
2. emacs --no-init
3. C-x b *scratch*
4. Copy the above example and paste into the buffer

I'm unable to identify which nixos-rebuild switch might be the cause since my emacs session is usually as long as the system uptime, during which many nixos-rebulids happen.

Notify maintainers
@lovek323 @peti @jwiegley @adisbladis

Metadata

 - system: `"x86_64-linux"`
 - host os: `Linux 5.4.54, NixOS, 20.03.2685.977000f149b (Markhor)`
 - multi-user?: `yes`
 - sandbox: `yes`
 - version: `nix-env (Nix) 2.3.6`
 - channels(root): `"nixos-20.03.2685.977000f149b"`
 - channels(me): `"nixpkgs-20.09pre232692.7db146538e4, nixos-20.03-20.03.2351.f8248ab6d9e"`
 - nixpkgs: `/home/yurb/.nix-defexpr/channels/nixpkgs`

Maintainer information:

# a list of nixpkgs attributes affected by the problem
attribute: emacs

[yurkobb]

Additional info:

1. seems to also affect +
2. doesn't affect session running in terminal with emacs -nw

[yurkobb]

Did another test - deleted ~/.cache/fontconfig/, ~/.gtkrc-2.0 and ~/.config/gtk-3.0/settings.ini, things went back to normal. Closing for now.