Call out to binutils' dlltool for raw-dylib on windows-gnu platforms.

compiler/rustc_interface/src/tests.rs

@@ -640,6 +640,7 @@ fn test_debugging_options_tracking_hash() {
     untracked!(borrowck, String::from("other"));
     untracked!(deduplicate_diagnostics, false);
     untracked!(dep_tasks, true);
+    untracked!(dlltool, Some(PathBuf::from("custom_dlltool.exe")));
     untracked!(dont_buffer_diagnostics, true);
     untracked!(dump_dep_graph, true);
     untracked!(dump_mir, Some(String::from("abc")));