Add regression test for OOM issue on EarlyLintPass ICE

Author: flip1995

tests/ui/treat-err-as-bug/panic-causes-oom-112708.rs

@@ -0,0 +1,11 @@
+// compile-flags: -Ztreat-err-as-bug
+// dont-check-failure-status
+// error-pattern: aborting due to `-Z treat-err-as-bug=1`
+// normalize-stderr-test "note: .*\n\n" -> ""
+// normalize-stderr-test "thread 'rustc' panicked.*\n" -> ""
+// rustc-env:RUST_BACKTRACE=0
+
+fn main() {
+    #[deny(while_true)]
+    while true {}
+}

tests/ui/treat-err-as-bug/panic-causes-oom-112708.stderr

@@ -0,0 +1,16 @@
+error: denote infinite loops with `loop { ... }`
+  --> $DIR/panic-causes-oom-112708.rs:10:5
+   |
+LL |     while true {}
+   |     ^^^^^^^^^^ help: use `loop`
+   |
+note: the lint level is defined here
+  --> $DIR/panic-causes-oom-112708.rs:9:12
+   |
+LL |     #[deny(while_true)]
+   |            ^^^^^^^^^^
+
+error: the compiler unexpectedly panicked. this is a bug.
+
+query stack during panic:
+thread panicked while processing panic. aborting.