Allow zero analyzer args in build mode.

pkg/analyzer_cli/test/options_test.dart

Index: pkg/analyzer_cli/test/options_test.dart
diff --git a/pkg/analyzer_cli/test/options_test.dart b/pkg/analyzer_cli/test/options_test.dart
index 620c047042f65e7f982aec22264bd9e70eed7d93..29bde19673e48370cb1ff987034fca81caf8baa4 100644
--- a/pkg/analyzer_cli/test/options_test.dart
+++ b/pkg/analyzer_cli/test/options_test.dart
@@ -257,6 +257,12 @@ class CommandLineOptionsTest extends AbstractStatusTest {
     expect(options.buildMode, isTrue);
   }
 
+  test_buildMode_allowsEmptyFileList() {
+    _parse(['--build-mode']);
+    expect(options.buildMode, isTrue);
+    expect(options.sourceFiles, isEmpty);
+  }
+
   test_buildSummaryFallback() {
     _parse([
       '--build-mode',