Set env vars for location of VC++ compiler.

test_scripts/automation/Windows/run-cmake.bat

@@ -13,8 +13,20 @@ if "%BUILD_PACKAGE%"=="Yes" (
 set OLD_DIR=%CD%
 
 cd %LLVM_OBJ_DIR%
+
+rem Set up the environment so CMake can find the Visual C++ compiler.
+setlocal
+for /f "usebackq tokens=*" %%i in (`vswhere -latest -products * -requires Microsoft.VisualStudio.Component.VC.Tools.x86.x64 -property installationPath`) do (
+  set InstallDir=%%i
+)
+
+if exist "%InstallDir%\VC\Auxiliary\Build" (
+  "%InstallDir%\VC\Auxiliary\BuildC\vcvars32.bat
+)
+
 cmake -G Ninja %EXTRA_FLAGS% -DCMAKE_BUILD_TYPE=%BUILDCONFIGURATION% DLLVM_ENABLE_PROJECTS=clang -DLLVM_INSTALL_TOOLCHAIN_ONLY=ON %BUILD_SOURCESDIRECTORY%\checkedc-llvm-project\llvm 
 if ERRORLEVEL 1 (goto cmdfailed)
+endlocal
 
 :succeeded
   cd %OLD_DIR%