date-check: rustc_codegen_ssa is still alive

Latest reference on it I could find on zulip:
https://rust-lang.zulipchat.com/#narrow/stream/131828-t-compiler/topic/Cursed.3A.20no_core.20Add.20on.20primitive.20int.20returning.20Option.3C.3E/near/287514393

Author: tshepang

src/backend/backend-agnostic.md

@@ -2,7 +2,7 @@
 
 <!-- toc -->
 
-As of <!-- date-check --> October 2021, `rustc_codegen_ssa` provides an
+As of <!-- date-check --> Aug 2022, `rustc_codegen_ssa` provides an
 abstract interface for all backends to implement, to allow other codegen
 backends (e.g. [Cranelift]).