Azure Pipelines: use "clang-cl" for Windows builds

Now that we can successfully compile with Clang, there's probably no reason to stick with MSVC.

.ci/azure-pipelines-win-steps.yml

@@ -1,6 +1,8 @@
 parameters:
 - name: architecture
   type: string
+- name: compilerPath
+  type: string
 - name: vcpkgTriplet
   type: string
 - name: vcvarsPath
@@ -18,7 +20,7 @@ steps:
   displayName: 'Prepare environment'
 - script: |
     call "${{parameters.vcvarsPath}}"
-    cmake -G "Ninja" -DCMAKE_TOOLCHAIN_FILE=C:/vcpkg/scripts/buildsystems/vcpkg.cmake -DVCPKG_TARGET_TRIPLET=${{parameters.vcpkgTriplet}} -DCMAKE_BUILD_TYPE=RelWithDebInfo -DCMAKE_C_COMPILER=cl -DCMAKE_CXX_COMPILER=cl $(Build.SourcesDirectory)
+    cmake -G "Ninja" -DCMAKE_TOOLCHAIN_FILE=C:/vcpkg/scripts/buildsystems/vcpkg.cmake -DVCPKG_TARGET_TRIPLET=${{parameters.vcpkgTriplet}} -DCMAKE_BUILD_TYPE=RelWithDebInfo -DCMAKE_C_COMPILER="${{parameters.compilerPath}}" -DCMAKE_CXX_COMPILER="${{parameters.compilerPath}}" $(Build.SourcesDirectory)
     cmake --build .
   workingDirectory: $(Build.BinariesDirectory)
   displayName: 'Build'

.ci/azure-pipelines-win.yml

@@ -7,6 +7,7 @@ jobs:
   - template: "azure-pipelines-win-steps.yml"
     parameters:
       architecture: "x86_64"
+      compilerPath: "C:/Program Files (x86)/Microsoft Visual Studio/2019/Enterprise/VC/Tools/Llvm/x64/bin/clang-cl.exe"
       vcpkgTriplet: "x64-windows-static-md"
       vcvarsPath: "C:/Program Files (x86)/Microsoft Visual Studio/2019/Enterprise/VC/Auxiliary/Build/vcvars64.bat"
 - job: windows_x86
@@ -17,5 +18,6 @@ jobs:
   - template: "azure-pipelines-win-steps.yml"
     parameters:
       architecture: "x86"
+      compilerPath: "C:/Program Files (x86)/Microsoft Visual Studio/2019/Enterprise/VC/Tools/Llvm/bin/clang-cl.exe"
       vcpkgTriplet: "x86-windows-static-md"
       vcvarsPath: "C:/Program Files (x86)/Microsoft Visual Studio/2019/Enterprise/VC/Auxiliary/Build/vcvarsamd64_x86.bat"