cgit's highlighter script supports newer highlight versions, but the config has
to be patched to enable that instead of the legacy version, which does not ship
with Gentoo any more. See: https://bugs.gentoo.org/962035

--- a/filters/syntax-highlighting.sh
+++ b/filters/syntax-highlighting.sh
@@ -115,7 +115,7 @@
 # found (for example) on EPEL 6.
 #
 # This is for version 2
-exec highlight --force -f -I -X -S "$EXTENSION" 2>/dev/null
+#exec highlight --force -f -I -X -S "$EXTENSION" 2>/dev/null
 
 # This is for version 3
-#exec highlight --force -f -I -O xhtml -S "$EXTENSION" 2>/dev/null
+exec highlight --force -f -I -O xhtml -S "$EXTENSION" 2>/dev/null