emit an error if we can't find a path to the self-contained linker

compiler/rustc_codegen_ssa/messages.ftl

@@ -212,6 +212,8 @@ codegen_ssa_rlib_only_rmeta_found = could not find rlib for: `{$crate_name}`, fo
 
 codegen_ssa_select_cpp_build_tool_workload = in the Visual Studio installer, ensure the "C++ build tools" workload is selected
 
+codegen_ssa_self_contained_linker_missing = the self-contained linker was requested, but it wasn't found in the target's sysroot, or in rustc's sysroot
+
 codegen_ssa_shuffle_indices_evaluation = could not evaluate shuffle_indices at compile time
 
 codegen_ssa_specify_libraries_to_link = use the `-l` flag to specify native libraries to link

compiler/rustc_codegen_ssa/src/back/link.rs

@@ -3138,9 +3138,9 @@ fn add_lld_args(
             }
         }
         if !linker_path_exists {
-            // As an additional sanity check, we do nothing if the sysroot doesn't contain the
-            // linker path at all.
-            return;
+            // As a sanity check, we emit an error if none of these paths exist: we want
+            // self-contained linking and have no linker.
+            sess.dcx().emit_fatal(errors::SelfContainedLinkerMissing);
         }
     }
 

compiler/rustc_codegen_ssa/src/errors.rs

@@ -413,6 +413,10 @@ pub struct UnableToExeLinker {
 #[diag(codegen_ssa_msvc_missing_linker)]
 pub struct MsvcMissingLinker;
 
+#[derive(Diagnostic)]
+#[diag(codegen_ssa_self_contained_linker_missing)]
+pub struct SelfContainedLinkerMissing;
+
 #[derive(Diagnostic)]
 #[diag(codegen_ssa_check_installed_visual_studio)]
 pub struct CheckInstalledVisualStudio;