Like many C hacks, this is a fun one, but hacks like this should absolutely be avoided for any serious C code–the magic is simply not worth the potential bugs!
PuTTY is written in a Duff's Device co-routine hack on steroids that I'm sure someone at one point said "should absolutely be avoided for any serious C code–the magic is simply not worth the potential bugs!"! And PuTTY is no small program, and it's very successful.
One person's hack-that-should-be-avoided-at-all-costs can be someone else's secret sauce.