Bug 1688235 - Allow warnings in our forked version of autcfg 0.1.6. r=firefox-build-system-reviewers,mhentges

These show up after bug 1685697 since now cargo thinks the code is ours.

Just prevent them from showing up since they're not useful nor we want
to fix them (they're fixed in more recent versions of the crate).

Differential Revision: https://phabricator.services.mozilla.com/D102775

third_party/rust/autocfg-0.1.6/src/lib.rs

@@ -40,6 +40,7 @@
 #![allow(unknown_lints)]
 #![allow(bare_trait_objects)]
 #![allow(ellipsis_inclusive_range_patterns)]
+#![allow(warnings)]
 
 use std::env;
 use std::ffi::OsString;