Spartan-6 LVCMOS33 input pin: can it take 5V without damage?
Yes.  There are ESD protection diodes to Vccio and these will turn on if the pin is supplied with a voltage higher than Vccio.  It may be possible to add a series current limiting resistor and use the ESD protection diode is a clamp, but this is not recommended.  You should look in to using some sort of external level shift circuit to prevent damage to the FPGA pins.