Tidy and auxiliary crate fixes for tests/ui/issues rehoming

Author: Oneirical

src/tools/tidy/src/issues.txt

@@ -17,7 +17,7 @@ use ignore::Walk;
 const ENTRY_LIMIT: u32 = 901;
 // FIXME: The following limits should be reduced eventually.
 
-const ISSUES_ENTRY_LIMIT: u32 = 1619;
+const ISSUES_ENTRY_LIMIT: u32 = 1386;
 
 const EXPECTED_TEST_FILE_EXTENSIONS: &[&str] = &[
     "rs",     // test source files

src/tools/tidy/src/ui_tests.rs

@@ -3,3 +3,5 @@ fn main() {
     let value = [7u8];
     while let Some(0) = value.get(0) {} //~ ERROR invalid left-hand side of assignment
 }
+
+// https://github.com/rust-lang/rust/issues/77218