Rollup merge of #123373 - onur-ozkan:skip-codegen, r=Mark-Simulacrum

skip Codegen{GCC,Cranelift} when using CI rustc

CI rustc uses the default codegen backend, therefore we can't run `CodegenGCC` and `CodegenCranelift` tests when using it.

cc `@bjorn3` (to make sure I am not doing anything wrong)

Fixes #123331

src/bootstrap/src/core/build_steps/test.rs

@@ -3300,6 +3300,11 @@ impl Step for CodegenCranelift {
             return;
         }
 
+        if builder.download_rustc() {
+            builder.info("CI rustc uses the default codegen backend. skipping");
+            return;
+        }
+
         if !target_supports_cranelift_backend(run.target) {
             builder.info("target not supported by rustc_codegen_cranelift. skipping");
             return;
@@ -3421,6 +3426,11 @@ impl Step for CodegenGCC {
             return;
         }
 
+        if builder.download_rustc() {
+            builder.info("CI rustc uses the default codegen backend. skipping");
+            return;
+        }
+
         let triple = run.target.triple;
         let target_supported =
             if triple.contains("linux") { triple.contains("x86_64") } else { false };