[test/win] Use correct cdb.exe on ARM64.

See https://dart-ci.appspot.com/log/vm-win-release-arm64/vm-win-release-arm64/3854/vm/cc/IsolateReload_RegressB179030011 for example of currently incorrect behavior where x86 is used instead of arm64.

TEST=ci

Change-Id: I8e725a1bca39dcdd67ea856b7ebbea24e750dfda
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/420501
Commit-Queue: Alexander Aprelev <aam@google.com>
Reviewed-by: Siva Annamalai <asiva@google.com>

pkg/test_runner/lib/src/test_case.dart

@@ -266,11 +266,12 @@ class RunningProcess {
                 command.executable.contains("SIMARM64") ||
                 command.executable.contains("SIMARM64C") ||
                 command.executable.contains("SIMRISCV64");
+            var isARM64 = !isX64 && command.executable.contains("ARM64");
             if (configuration.windowsSdkPath != null) {
               executable = [
                 configuration.windowsSdkPath!,
                 'Debuggers',
-                if (isX64) 'x64' else 'x86',
+                if (isX64) 'x64' else if (isARM64) 'arm64' else 'x86',
                 'cdb.exe',
               ].join('\\');
               diagnostics.add("Using $executable to print stack traces");