Port Windows MSVC and ClangCL Bazel tests to GitHub Actions.

This adds the `windows` job matrix to `.github/workflows/ci.yml` and `build:windows-msvc` / `build:windows-clangcl` configurations to `.bazelrc` to mirror the 7 Windows Bazel Kokoro jobs.

PiperOrigin-RevId: 1002818299

.bazelrc

diff --git a/.bazelrc b/.bazelrc
index c39ac4e..91d4da9 100644
--- a/.bazelrc
+++ b/.bazelrc
@@ -37,6 +37,19 @@
 build:linux --per_file_copt=external/.*@-w
 build:linux --host_per_file_copt=external/.*@-w
 
+# Configure our Windows MSVC and ClangCL setup.
+common:windows-msvc --enable_runfiles
+build:windows-msvc --cxxopt=/std:c++17 --host_cxxopt=/std:c++17
+build:windows-msvc --copt=/WX
+build:windows-msvc --per_file_copt=external/.*@/w
+build:windows-msvc --host_per_file_copt=external/.*@/w
+
+build:windows-clangcl --config=windows-msvc
+build:windows-clangcl --compiler=clang-cl
+build:windows-clangcl --copt=-Wno-microsoft-cast
+build:windows-clangcl --extra_execution_platforms=//:x64_windows-clang-cl
+build:windows-clangcl --extra_toolchains=@local_config_cc//:cc-toolchain-x64_windows-clang-cl
+
 build:gcc --config=linux --platforms=//ci:linux_gcc
 build:gcc-exceptions --config=gcc --copt=-fexceptions
 build:clang --config=linux --platforms=//ci:linux_clang --conlyopt=-Wno-unused-command-line-argument
@@ -62,6 +75,13 @@
 test:tsan --test_tag_filters=-benchmark,-notsan
 
 # Remote build configuration for CI.
+build:remote-cache --remote_cache=grpcs://us-east1-remotebuildexecution.googleapis.com
+build:remote-cache --remote_instance_name=projects/google.com:absl-177019/instances/absl-ci-east
+build:remote-cache --remote_timeout=1200 --bes_timeout=600s
+build:remote-cache --remote_download_minimal
+# Retry up for up to 15 minutes under heavy load (exponential backoff).
+build:remote-cache --remote_retries=20 --remote_retry_max_delay=60s
+
 build:remote-base --define=EXECUTOR=remote
 build:remote-base --remote_timeout=1200 --bes_timeout=600s
 build:remote-base --jobs=50

.github/workflows/ci.yml

diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 0e9e9b9..4de4e8f 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -46,7 +46,7 @@
 jobs:
   # Mirrors the 11 Linux Bazel Kokoro jobs (parallelized to 1 job per Bazel
   # invocation). Not yet covered here:
-  #   - macOS Bazel and Windows Bazel Kokoro jobs
+  #   - macOS Kokoro jobs
   linux:
     name: Linux ${{ matrix.config.name }} Bazel
     strategy:
@@ -151,10 +151,39 @@
       link_modes: ${{ matrix.config.link_modes || '["static", "shared", "monolithic-shared"]' }}
       install_test: ${{ matrix.config.install_test || false }}
 
+  windows:
+    name: Windows ${{ matrix.config.name }} Bazel
+    strategy:
+      fail-fast: false  # Don't cancel all jobs if one fails.
+      matrix:
+        config:
+          # windows-msvc-2022-cxx{17,20}-{dbg,opt}-bazel.cfg
+          - name: MSVC 2022
+            toolchain: windows-msvc
+          # windows-msvc-2022-alternate-options-cxx{17,20}-dbg-bazel.cfg (dbg only)
+          - name: MSVC 2022 Alternate Options
+            toolchain: windows-msvc
+            alternate_options: true
+            compilation_modes: '["dbg"]'
+          # windows-clangcl-cxx17-fastbuild-bazel.cfg
+          - name: ClangCL
+            toolchain: windows-clangcl
+            stds: '["c++17"]'
+            compilation_modes: '["fastbuild"]'
+    uses: ./.github/workflows/bazel.yml
+    secrets: inherit
+    with:
+      os: windows-2022
+      toolchain: ${{ matrix.config.toolchain }}
+      remote_config: remote-cache
+      alternate_options: ${{ matrix.config.alternate_options || false }}
+      stds: ${{ matrix.config.stds || '["c++17", "c++20"]' }}
+      compilation_modes: ${{ matrix.config.compilation_modes || '["dbg", "opt"]' }}
+
   # Provide a single predictably-named job for copybara to look for
   all-blocking-tests:
     name: All Blocking Tests
-    needs: [linux, cmake]
+    needs: [linux, cmake, windows]
     runs-on: ubuntu-latest
     steps:
       - name: Check for cancellations