skip workspace-hungry operations on 32bit for now

(actually not on 32bit, but where the default workspace is low)

Ref #3203

bin/varnishtest/tests/v00004.vtc

@@ -154,6 +154,10 @@ varnish v1 -vcl+backend {
 	sub recv9 {
 		std.log("STK recv9 " + debug.stk() + " WS " +
 		    vtc.workspace_free(client));
+		if (vtc.workspace_free(client) < 48 * 1024) {
+			std.log("XXX #3203 skipping");
+			return;
+		}
 		set req.http.regex = regsub(req.http.cookie, "(.*)", "\1\1\1\1\1\1\1\1");
 		std.log("WS " + vtc.workspace_free(client));
 		# hey geoff, this is deliberate