Updated C code sample

This code comes from the compiler-tests repo: https://github.com/Microsoft/compiler-tests/blob/master/seh/xcpt4u.c

If there's a problem with that source for some reason, the Windows-driver-samples repo also has some C code: https://github.com/Microsoft/Windows-driver-samples/blob/master/network/modem/fakemodem/ioctl.c

Fixes microsoft#11