bug#43177: Bug: Emacs 27.1 hangs forever in `FcCharSetSubtractCount' from '/usr/lib/libfontconfig.so.1'

[Alexander Shukaev <emacs@Alexander.Shukaev.name>]

Not sure how to debug further:

(gdb) f 7
#7  0x0000555555aa48f0 in ftcrfont_open (f=0x555556521410, 
entity=XIL(0x55555aa0d7c5), pixel_size=21) at ftcrfont.c:137
137	  match = FcFontMatch (NULL, pat, &result);
(gdb) p pat
$1 = (FcPattern *) 0x55556845efb0
(gdb) p *pat
$2 = <incomplete type>
(gdb) info locals
result = FcResultNoMatch
val = XIL(0x5555658e2a23)
filename = XIL(0x55555ba4d1e4)
font_object = XIL(0x555565b558a5)
pat = 0x55556845efb0
match = 0x55555be76210
ftcrfont_info = 0x555565b558a0
font = 0x555565b558a0
size = 21
font_face = 0x55555ef899f0
extents = {
   ascent = 18,
   descent = 3.0000000000000004,
   height = 20,
   max_x_advance = 4.6355841119114706e-310,
   max_y_advance = 6.9533558052579579e-310
}
ft_face = 0x55555a74ab50
matrix = 0x555564edf50f
font_matrix = {
   xx = 4.6355841119112235e-310,
   yx = 4.6355841119114706e-310,
   xy = 4.6355707518995349e-310,
   yy = 2.000000208656282,
   x0 = 6.9533558052595389e-310,
   y0 = 4.6355707518839718e-310
}
ctm = {
   xx = 4.6355707529419146e-310,
   yx = 4.6355841119114706e-310,
   xy = 6.9533558052611199e-310,
   yy = 4.6355707529569342e-310,
   x0 = 0,
   y0 = 4.6355841119114706e-310
}
options = 0x555557584e40
scaled_font = 0x555558791990
stack_glyph = {
   index = 127,
   x = 0,
   y = 0
}