ci: build Windows ARM64 with CMake 4.3 like the other platforms (#16052)

The ARM64 jobs pinned CMake 3.31 because CMake 4 dropped pre-3.5 policy
compatibility and its ARMASM support broke Boost.Context. Both are
handled now. deps/CMakeLists.txt sets CMAKE_POLICY_VERSION_MINIMUM on
CMake 4, and Boost.Context uses the winfib implementation on ARM64, so
nothing assembles with armasm.

CMake 3.31 also predates VS 2026. Its InstallRequiredSystemLibraries
treats the v145 toolset as v143, searches only the VS 2017-2022 install
directories and finds no runtime, so the ARM64 installer ships without
msvcp140.dll and vcruntime140.dll. CMake 4.2 and newer find the VC145
redistributable.

get-cmake also installs Ninja, so the ARM64 jobs now use its latest
release instead of the one already on the runner, as x64 does.

The install now fails when InstallRequiredSystemLibraries returns no
msvcp140.dll or vcruntime140.dll, after a configure warning naming the
CMake and MSVC versions. A CMake that predates the Visual Studio in use,
on a developer machine or after the next runner image update, then
stops the installer build instead of shipping one that cannot start.

The build_win.bat prerequisite installer drops its matching 3.31.8 pin.

.github/workflows/build_deps.yml

@@ -49,28 +49,11 @@ jobs:
           key: ${{ inputs.cache-key }}
 
       - uses: lukka/get-cmake@latest
-        # The windows-11-arm runner needs CMake <= 3.31 (handled in the next step).
-        if: ${{ !(runner.os == 'Windows' && inputs.arch == 'arm64') }}
         with:
           cmakeVersion: "~4.3.0"  # use most recent 4.3.x version
           useLocalCache: true         # <--= Use the local cache (default is 'false').
           useCloudCache: true
 
-      - name: Install CMake 3.31.x (Windows ARM64)
-        # windows-11-arm ships CMake 4.x, which removed pre-3.5 policy
-        # compatibility AND has incomplete ASM_ARMASM linker modules
-        # (breaks Boost.Context on ARM64). Pin to the last 3.x release.
-        if: runner.os == 'Windows' && inputs.arch == 'arm64'
-        shell: pwsh
-        run: |
-          $ver = "3.31.6"
-          $url = "https://github.com/Kitware/CMake/releases/download/v$ver/cmake-$ver-windows-arm64.zip"
-          Invoke-WebRequest -Uri $url -OutFile "$env:RUNNER_TEMP\cmake.zip"
-          Expand-Archive -Path "$env:RUNNER_TEMP\cmake.zip" -DestinationPath "$env:RUNNER_TEMP\cmake" -Force
-          $cmakeBin = "$env:RUNNER_TEMP\cmake\cmake-$ver-windows-arm64\bin"
-          if (-not (Test-Path "$cmakeBin\cmake.exe")) { throw "cmake.exe not found at $cmakeBin" }
-          Add-Content -Path $env:GITHUB_PATH -Value $cmakeBin
-
       - name: setup dev on Windows
         if: runner.os == 'Windows'
         uses: microsoft/setup-msbuild@v3

.github/workflows/build_orca.yml

@@ -54,28 +54,11 @@ jobs:
           fail-on-cache-miss: true
 
       - uses: lukka/get-cmake@latest
-        # The windows-11-arm runner needs CMake <= 3.31 (handled in the next step).
-        if: ${{ !(runner.os == 'Windows' && inputs.arch == 'arm64') }}
         with:
           cmakeVersion: "~4.3.0"  # use most recent 4.3.x version
           useLocalCache: true         # <--= Use the local cache (default is 'false').
           useCloudCache: true
 
-      - name: Install CMake 3.31.x (Windows ARM64)
-        # windows-11-arm ships CMake 4.x, which removed pre-3.5 policy
-        # compatibility AND has incomplete ASM_ARMASM linker modules
-        # (breaks Boost.Context on ARM64). Pin to the last 3.x release.
-        if: runner.os == 'Windows' && inputs.arch == 'arm64'
-        shell: pwsh
-        run: |
-          $ver = "3.31.6"
-          $url = "https://github.com/Kitware/CMake/releases/download/v$ver/cmake-$ver-windows-arm64.zip"
-          Invoke-WebRequest -Uri $url -OutFile "$env:RUNNER_TEMP\cmake.zip"
-          Expand-Archive -Path "$env:RUNNER_TEMP\cmake.zip" -DestinationPath "$env:RUNNER_TEMP\cmake" -Force
-          $cmakeBin = "$env:RUNNER_TEMP\cmake\cmake-$ver-windows-arm64\bin"
-          if (-not (Test-Path "$cmakeBin\cmake.exe")) { throw "cmake.exe not found at $cmakeBin" }
-          Add-Content -Path $env:GITHUB_PATH -Value $cmakeBin
-
       # Compiler cache. Pushes save it, so main keeps it warm; pull requests
       # restore it and discard what they compiled. Objects are keyed on the
       # preprocessed source, the compiler and the flags, so a leg only ever