Try to manually run cmake on Windows.

azure-pipelines.yml

@@ -47,9 +47,15 @@ jobs:
         choco.exe install ninja
         choco.exe install llvm
 
-    - task: CMake@1
-      inputs:
-          cmakeArgs: '.. -G Ninja -DCMAKE_C_COMPILER="c:/Program Files/LLVM/bin/clang-cl.exe" -DCMAKE_CXX_COMPILER="c:/Program Files/LLVM/bin/clang-cl.exe"'
+
+
+    - script: |
+        "C:\Program Files (x86)\Microsoft Visual Studio 12.0\VC\vcvarsall.bat" x64
+        cmake .. -G Ninja -DCMAKE_C_COMPILER="c:/Program Files/LLVM/bin/clang-cl.exe" -DCMAKE_CXX_COMPILER="c:/Program Files/LLVM/bin/clang-cl.exe"
+
+      workingDirectory: build
+      failOnStderr: true
+      displayName: 'CMake'
 
     - script: |
         set CCC_OVERRIDE_OPTIONS=x-TC x-TP x/TC x/TP