message: Use CI variable to find ISPC
diff: @@ -18,12 +18,21 @@ Set-Location "${ROOT_DIR}/${BUILD_DIR}"
  cmake --version
  -# Set up build.
  +
  +if (Test-Path Env:OIDN_ISPC_EXECUTABLE_WINDOWS) {
  + cmake -L `
  + -G "${GENERATOR}" `
  + -T "${TOOLCHAIN}" `
  + -D TBB_ROOT="${TBB_DIR}" `
  + -D ISPC_EXECUTABLE="${Env:OIDN_ISPC_EXECUTABLE_WINDOWS}" `
  + ..
  +} else {
  cmake -L `
  -G "${GENERATOR}" `
  -T "${TOOLCHAIN}" `
  -D TBB_ROOT=${TBB_DIR} `
  ..
  +}
  if (!$?) { Exit $LASTEXITCODE }
  