Detect attempt to use var-args in closure
```
error: unexpected `...`
--> $DIR/no-closure.rs:11:14
|
LL | let f = |...| {};
| ^^^ not a valid pattern
|
= note: only `extern "C"` and `extern "C-unwind"` functions may have a C variable argument list
error: unexpected `...`
--> $DIR/no-closure.rs:16:17
|
LL | let f = |_: ...| {};
| ^^^
|
= note: only `extern "C"` and `extern "C-unwind"` functions may have a C variable argument list
```
Fixrust-lang/rust#146489, when trying to use c-style var-args in a closure. We emit a more targeted message. We also silence inference errors when the pattern is `PatKind::Err`.
61f53585aa