Roll Clang from d0ddae678e3f to 637e9bc0f763

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@rotations.google.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://issues.skia.org/issues/new?component=1389291&template=1850622

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-linux-arm64-try;luci.dart.try:dart-sdk-mac-try;luci.dart.try:dart-sdk-mac-arm64-try;luci.dart.try:dart-sdk-win-try;luci.dart.try:vm-asan-mac-release-arm64-try
Change-Id: I32d58c0af3aaaeda8d36e6b7f58b0a3784a88a3d
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/490440
Reviewed-by: Alexander Aprelev <aam@google.com>
Reviewed-by: Alexander Markov <alexmarkov@google.com>
Commit-Queue: Alexander Markov <alexmarkov@google.com>

DEPS

@@ -80,7 +80,7 @@ vars = {
   "jsc_tag": "version:308651",
 
   # https://chrome-infra-packages.appspot.com/p/fuchsia/third_party/clang
-  "clang_version": "git_revision:d0ddae678e3f634c988542dfbdde1dd0afe66344",
+  "clang_version": "git_revision:637e9bc0f7637f5da0883c99c4a782f3e8d5e20a",
 
   # https://chrome-infra-packages.appspot.com/p/gn/gn
   "gn_version": "git_revision:b2ac0e7a9089039e62b84d246eca83f84c540f76",