Add note about writing native-static-libs to file

compiler/rustc_codegen_ssa/messages.ftl

@@ -197,6 +197,8 @@ codegen_ssa_specify_libraries_to_link = use the `-l` flag to specify native libr
 
 codegen_ssa_static_library_native_artifacts = Link against the following native artifacts when linking against this static library. The order and any duplication can be significant on some platforms.
 
+codegen_ssa_static_library_native_artifacts_to_file = Native artifacts to link against have been written to {$path}. The order and any duplication can be significant on some platforms.
+
 codegen_ssa_stripping_debug_info_failed = stripping debug info with `{$util}` failed: {$status}
     .note = {$output}
 

compiler/rustc_codegen_ssa/src/back/link.rs

@@ -1467,7 +1467,12 @@ fn print_native_static_libs(
     }
 
     match out {
-        OutFileName::Real(_) => out.overwrite(&lib_args.join(" "), sess),
+        OutFileName::Real(path) => {
+            out.overwrite(&lib_args.join(" "), sess);
+            if !lib_args.is_empty() {
+                sess.emit_note(errors::StaticLibraryNativeArtifactsToFile { path });
+            }
+        }
         OutFileName::Stdout => {
             if !lib_args.is_empty() {
                 sess.emit_note(errors::StaticLibraryNativeArtifacts);

compiler/rustc_codegen_ssa/src/errors.rs

@@ -455,6 +455,12 @@ pub struct LinkerFileStem;
 #[diag(codegen_ssa_static_library_native_artifacts)]
 pub struct StaticLibraryNativeArtifacts;
 
+#[derive(Diagnostic)]
+#[diag(codegen_ssa_static_library_native_artifacts_to_file)]
+pub struct StaticLibraryNativeArtifactsToFile<'a> {
+    pub path: &'a Path,
+}
+
 #[derive(Diagnostic)]
 #[diag(codegen_ssa_link_script_unavailable)]
 pub struct LinkScriptUnavailable;