Do not recover when parsing stmt in cfg-eval.

tests/ui/cfg/cfg-stmt-recovery.rs

@@ -0,0 +1,13 @@
+// Verify that we do not ICE when failing to parse a statement in `cfg_eval`.
+
+#![feature(cfg_eval)]
+#![feature(stmt_expr_attributes)]
+
+#[cfg_eval]
+fn main() {
+    #[cfg_eval]
+    let _ = #[cfg(FALSE)] 0;
+    //~^ ERROR removing an expression is not supported in this position
+    //~| ERROR expected expression, found `;`
+    //~| ERROR removing an expression is not supported in this position
+}

tests/ui/cfg/cfg-stmt-recovery.stderr

@@ -0,0 +1,20 @@
+error: removing an expression is not supported in this position
+  --> $DIR/cfg-stmt-recovery.rs:9:13
+   |
+LL |     let _ = #[cfg(FALSE)] 0;
+   |             ^^^^^^^^^^^^^
+
+error: expected expression, found `;`
+  --> $DIR/cfg-stmt-recovery.rs:9:28
+   |
+LL |     let _ = #[cfg(FALSE)] 0;
+   |                            ^ expected expression
+
+error: removing an expression is not supported in this position
+  --> $DIR/cfg-stmt-recovery.rs:9:13
+   |
+LL |     let _ = #[cfg(FALSE)] 0;
+   |             ^^^^^^^^^^^^^
+
+error: aborting due to 3 previous errors
+