Ignore the output itself on `rustc-rust-log.rs` (added in rust-lang/rust#42737).

src/test/run-pass/rustc-rust-log.rs

@@ -8,6 +8,15 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+// This test is just checking that we won't ICE if logging is turned
+// on; don't bother trying to compare that (copious) output. (Note
+// also that this test potentially silly, since we do not build+test
+// debug versions of rustc as part of our continuous integration
+// process...)
+//
+// dont-check-compiler-stdout
+// dont-check-compiler-stderr
+
 // rustc-env:RUST_LOG=debug
 
 fn main() {}