Make --print=backend-has-zstd work by default on any backend

Using a defaulted `CodegenBackend` method that querying for zstd support should
automatically print a safe value of `false` on any backend that doesn't
specifically indicate the presence or absence of zstd.

Author: Zalathar

src/lib.rs

@@ -47,7 +47,7 @@ use rustc_codegen_ssa::{CodegenResults, TargetConfig};
 use rustc_log::tracing::info;
 use rustc_middle::dep_graph::{WorkProduct, WorkProductId};
 use rustc_session::Session;
-use rustc_session::config::{OutputFilenames, PrintKind, PrintRequest};
+use rustc_session::config::OutputFilenames;
 use rustc_span::{Symbol, sym};
 use rustc_target::spec::{Abi, Arch, Env, Os};
 
@@ -160,16 +160,6 @@ impl CodegenBackend for CraneliftCodegenBackend {
         }
     }
 
-    fn print(&self, req: &PrintRequest, out: &mut String, _sess: &Session) {
-        match req.kind {
-            // FIXME have a default impl that returns false
-            PrintKind::BackendHasZstd => {
-                out.push_str("false\n");
-            }
-            _ => {}
-        }
-    }
-
     fn target_config(&self, sess: &Session) -> TargetConfig {
         // FIXME return the actually used target features. this is necessary for #[cfg(target_feature)]
         let target_features = match sess.target.arch {