Problem reported by John ff in:
https://lists.gnu.org/r/emacs-devel/2018-04/msg00058.html
* src/ftfont.c (ftfont_spec_pattern) [!FC_COLOR]:
Don’t use FC_COLOR on older fontconfigs that don’t have it.
if (scalable >= 0
&& ! FcPatternAddBool (pattern, FC_SCALABLE, scalable ? FcTrue : FcFalse))
goto err;
-#ifdef HAVE_XFT
+#if defined HAVE_XFT && defined FC_COLOR
/* We really don't like color fonts, they cause Xft crashes. See
Bug#30874. */
if (Vxft_ignore_color_fonts