Make controlflow part of a function type

Change ty_fn to have a controlflow field. A 'controlflow' is
essentially a bit of data that says whether or not this function
never returns to the caller (if it never returns, that means it calls
"fail" or another "never-returns" function on every control path).

Also add syntax for annotating functions that never return:

fn foo() -> ! {
   fail;
}

for example. Functions marked with ! implicitly have a result type of
ty_bot, which is a new type that this commit also adds.

0 files changed, 0 insertions, 0 deletions