Only use dlltool.exe on MinGW if -Cdlltool is passed

compiler/rustc_codegen_ssa/src/back/archive.rs

@@ -87,12 +87,12 @@ pub trait ArchiveBuilderBuilder {
         items: Vec<ImportLibraryItem>,
         output_path: &Path,
     ) {
-        if common::is_mingw_gnu_toolchain(&sess.target) {
-            // The binutils linker used on -windows-gnu targets cannot read the import
-            // libraries generated by LLVM: in our attempts, the linker produced an .EXE
-            // that loaded but crashed with an AV upon calling one of the imported
-            // functions. Therefore, use binutils to create the import library instead,
-            // by writing a .DEF file to the temp dir and calling binutils's dlltool.
+        if common::is_mingw_gnu_toolchain(&sess.target) && sess.opts.cg.dlltool.is_some() {
+            // Previously we always used dlltool on -windows-gnu targets due to the binutils
+            // linker not entirely correctly handling import libraries generated by
+            // LLVM/ar_archive_writer. This has since been fixed. To ease the transition, will
+            // temporarily still use dlltool if explicitly specified, but use ar_archive_writer
+            // like on MSVC if not.
             create_mingw_dll_import_lib(sess, lib_name, items, output_path);
         } else {
             trace!("creating import library");