fontconfig: stop using xml:space; vital for nixos+2.11

This is a proper fix for problems described in ec985c8 .
The code is from @lethalman.

pkgs/development/libraries/fontconfig/make-fonts-conf.xsl

@@ -20,7 +20,7 @@
   <xsl:template match="/fontconfig">
 
     <fontconfig>
-      <xsl:copy-of select="child::node()[name() != 'dir' and name() != 'cachedir' and name() != 'include']" />
+      <xsl:apply-templates select="child::node()[name() != 'dir' and name() != 'cachedir' and name() != 'include']" />
 
       <include ignore_missing="yes">/etc/fonts/conf.d</include>
       <include><xsl:value-of select="$fontconfig" />/etc/fonts/conf.d</include>
@@ -40,4 +40,12 @@
 
   </xsl:template>
 
+
+  <!-- New fontconfig >=2.11 doesn't like xml:space added by xsl:copy-of -->
+  <xsl:template match="node()|@*">
+    <xsl:copy>
+      <xsl:apply-templates select="node()|@*[name() != 'xml:space']"/>
+    </xsl:copy>
+  </xsl:template>
+
 </xsl:stylesheet>