Now there is a Gulp configuration in which all the scripts are written into one .css file. But you need to separate the files with the suffix -ie (fname-ie.styl) and collect them separately, next to the (common) .min.css file.
gulp.task('styles', () => ( gulp.src('app/styles/*.styl') .pipe(stylus({ use: [ importIfExist(), rupture() ], 'include css': true })) .pipe(rename({suffix: '.min'})) .pipe(gulp.dest('dist/assets/styles')) ));