Roll Clang from 5344d8e10bb7 to 6d667d4b261e

If this roll has caused a breakage, revert this CL and stop the roller
using the controls here:
https://autoroll.skia.org/r/clang-dart-sdk
Please CC dart-engprod@google.com,dart-vm-gardener@grotations.appspotmail.com,dart-vm-team@google.com on the revert to ensure that a human
is aware of the problem.

To file a bug in Clang: https://bugs.fuchsia.dev/p/fuchsia/issues/list?q=component%3AToolchain
To file a bug in Dart SDK: https://github.com/dart-lang/sdk/issues

To report a problem with the AutoRoller itself, please file a bug:
https://bugs.chromium.org/p/skia/issues/entry?template=Autoroller+Bug

Documentation for the AutoRoller is here:
https://skia.googlesource.com/buildbot/+doc/main/autoroll/README.md

Cq-Include-Trybots: luci.dart.try:dart-sdk-linux-try;luci.dart.try:dart-sdk-mac-try;luci.dart.try:dart-sdk-mac-arm64-try;luci.dart.try:dart-sdk-win-try
Change-Id: Id139b808aa0ffde7eea75fa0b57d4ce6dd59fc5a
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/304440
Commit-Queue: Ryan Macnak <rmacnak@google.com>
Reviewed-by: Ryan Macnak <rmacnak@google.com>

DEPS

@@ -73,7 +73,7 @@ vars = {
   # The list of revisions for these tools comes from Fuchsia, here:
   # https://fuchsia.googlesource.com/integration/+/HEAD/toolchain
   # If there are problems with the toolchain, contact fuchsia-toolchain@.
-  "clang_version": "git_revision:5344d8e10bb7d8672d4bfae8adb010465470d51b",
+  "clang_version": "git_revision:6d667d4b261e81f325756fdfd5bb43b3b3d2451d",
   "gn_version": "git_revision:5a004f9427a050c6c393c07ddb85cba8ff3849fa",
 
   # Update from https://chrome-infra-packages.appspot.com/p/fuchsia/sdk/gn