cleanup Analyzer CLI and DDC arg parsing

pkg/analyzer/lib/src/command_line/arguments.dart

Index: pkg/analyzer/lib/src/command_line/arguments.dart
diff --git a/pkg/analyzer/lib/src/command_line/arguments.dart b/pkg/analyzer/lib/src/command_line/arguments.dart
index 6ad44aff58da60639e5960b8852e293c67c80017..5b43d3c2e489671794c6971205affe0e5f0ca587 100644
--- a/pkg/analyzer/lib/src/command_line/arguments.dart
+++ b/pkg/analyzer/lib/src/command_line/arguments.dart
@@ -184,7 +184,10 @@ List<String> extractDefinedVariables(
         remainingArgs.add(args[i++]);
       }
     } else if (arg.startsWith("-D")) {
-      if (i + 1 < count) {
+      int end = arg.indexOf('=');
+      if (end > 2) {
+        definedVariables[arg.substring(2, end)] = arg.substring(end + 1);
+      } else if (i + 1 < count) {
         definedVariables[arg.substring(2)] = args[++i];
       } else {
         remainingArgs.add(arg);