Apply workaround from rust-lang#72003 for rust-lang#56935

thomaseizinger · thomaseizinger · commit ff00ef4d6656 · 2021-01-29T14:56:37.000+11:00
Related: rust-lang#72017.
diff --git a/compiler/rustc_index/src/lib.rs b/compiler/rustc_index/src/lib.rs
@@ -8,3 +8,7 @@
 
 pub mod bit_set;
 pub mod vec;
+
+// FIXME(#56935): Work around ICEs during cross-compilation.
+#[allow(unused)]
+extern crate rustc_macros;
