EXTREMELY hacky fix

This runs _just_ enough of typeck that later queries don't panic.
Because this is in the same part of the compiler that errors on `impl
Trait`, this special-cases impl Trait for rustdoc and no one else.
Everything is fine.

src/test/rustdoc-ui/infinite-recursive-type-impl-trait.rs

@@ -0,0 +1,7 @@
+fn f() -> impl Sized {
+    enum E {
+    //~^ ERROR recursive type `f::E` has infinite size
+        V(E),
+    }
+    unimplemented!()
+}

src/test/rustdoc-ui/infinite-recursive-type-impl-trait.stderr

@@ -0,0 +1,17 @@
+error[E0072]: recursive type `f::E` has infinite size
+  --> $DIR/infinite-recursive-type-impl-trait.rs:2:5
+   |
+LL |     enum E {
+   |     ^^^^^^ recursive type has infinite size
+LL |
+LL |         V(E),
+   |           - recursive without indirection
+   |
+help: insert some indirection (e.g., a `Box`, `Rc`, or `&`) to make `f::E` representable
+   |
+LL |         V(Box<E>),
+   |           ^^^^ ^
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0072`.

src/test/rustdoc-ui/infinite-recursive-type.stderr

@@ -1,26 +1,17 @@
-error: internal compiler error[E0391]: cycle detected when computing `Sized` constraints for `E`
+error[E0072]: recursive type `E` has infinite size
   --> $DIR/infinite-recursive-type.rs:1:1
    |
 LL | enum E {
-   | ^^^^^^
+   | ^^^^^^ recursive type has infinite size
+LL |
+LL |     V(E),
+   |       - recursive without indirection
    |
-   = note: ...which again requires computing `Sized` constraints for `E`, completing the cycle
-   = note: cycle used when evaluating trait selection obligation `E: std::convert::From<E>`
-
-error: internal compiler error: TyKind::Error constructed but no error reported
+help: insert some indirection (e.g., a `Box`, `Rc`, or `&`) to make `E` representable
    |
-   = note: delayed at /home/joshua/rustc/src/librustc_session/session.rs:436:27
+LL |     V(Box<E>),
+   |       ^^^^ ^
 
-thread 'rustc' panicked at 'no errors encountered even though `delay_span_bug` issued', src/librustc_errors/lib.rs:366:17
-note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
-
-error: internal compiler error: unexpected panic
-
-note: the compiler unexpectedly panicked. this is a bug.
-
-note: we would appreciate a bug report: https://github.com/rust-lang/rust/issues/new?labels=C-bug%2C+I-ICE%2C+T-compiler&template=ice.md
-
-note: rustc 1.47.0-dev running on x86_64-unknown-linux-gnu
-
-note: compiler flags: -Z threads=1 -Z ui-testing -Z deduplicate-diagnostics=no -Z unstable-options -C debuginfo=0
+error: aborting due to previous error
 
+For more information about this error, try `rustc --explain E0072`.