SPEC.md allows `try` only inside a function returning an error union, but the
check sat in the FE_N_EXPR_STMT case, so it only ever saw a bare `try e;` and
walked past `var x = try e;` and `x = try e;`. Move it onto the try expression
in check_expr and drop the statement-level copy.
This could not land before M7: closing the hole forces m5/runtime.fe's `run` to
return an error union, and value returns from `-> !T` need contextual success
construction. That arrives with M7, and `run` is now `-> !i32`, so the rule can
be enforced. Supersedes the SPEC.AUDIT.md entry that recorded the blockage.
M1-M7: 183 passed.
coolguy
a2428ca5da