OK, but I guess what's really being relied on there is that it's syntactically still a single statement when you follow it with ';', whereas {...}; is two state

OK, but I guess what's really being relied on there is that it's syntactically still a single statement when you follow it with ';', whereas {...}; is two statements (which is what breaks the if-else). I just discovered that gcc also supports non-standard "statement expressions" of the form ({...}) which would serve the same purpose at the cost of portability.