Avoid error with old Bison versions

`api.token.raw` is only defined starting with Bison 3.5
Since it's not essential, define it on the command-line iff the Bison
version is sufficient.

src/check_bison_ver.sh

@@ -0,0 +1,7 @@
+#!/bin/sh
+bison -V | awk '
+/^bison.*[0-9]+(\.[0-9]+){1,2}$/ {
+	match($0, /[0-9]+(\.[0-9]+){1,2}$/);
+	split(substr($0, RSTART), ver, ".");
+	if (ver[1] == major && ver[2] >= minor) { exit 0 } else { exit 1 }
+}' major="$1" minor="$2"