Step 5: Add clang cl pipeline for Windows

[wrowe]

Commit Message: Step 5: Add clang cl pipeline for Windows
Additional Description:

Now that we have regenerated envoy build tools to update bazel and llvm, introduce a clang-cl pipeline based on clang-cl

Co-authored-by: Sunjay Bhatia sunjayb@vmware.com

Risk Level: low (new facility)
Testing: local
Docs Changes: TBD
Release Notes: TBD
Platform Specific Features: Windows clang-cl compilation
Requires #13688
Fixes #11974

[repokitteh-read-only]

CC @envoyproxy/dependency-shepherds: Your approval is needed for changes made to (bazel/.*repos.*\.bzl)|(bazel/dependency_imports\.bzl)|(api/bazel/.*\.bzl)|(.*/requirements\.txt)|(.*\.patch).

🐱

Caused by: #14135 was opened by wrowe.

see: more, trace.

[wrowe]

The most recent push dropped the step 2 patch of the bazel version number change, that's still ambiguous.

[repokitteh-read-only]

Retrying Azure Pipelines:
Retried failed jobs in: envoy-presubmit

🐱

Caused by: a #14135 (comment) was created by @wrowe.

see: more, trace.

[wrowe]

Now that lizan picked up step 4, going to retry a couple times with the new tooling. We did something specific in this patch which can be changed... the clang pipelines runs after the msvc pipeline, mostly to give the msvc build all the compute it needs to get finished. But depending on how gcp rbe behaves, we could invoke them in parallel.

[wrowe]

This is being rescheduled to 1.18-dev, and will be moved to the windows-ga
milestone once the interesting half... #14608 has been merged, and
this commit rebased down to simply a new pipeline.

The flake and the fail noted from //test/common/network:dns_impl_test and //test/extensions/filters/network/sni_dynamic_forward_proxy:proxy_filter_integration_test
need to be added to this patch, but specific only to clang-cl builds, since msvc-cl
builds seem to be unaffected.

[wrowe]

This patch was split into 14608 (applied) and 14668 (draft).

Closing this ticket to retire the github org it was pulled from.