message: Return undefined explicitly when OS is not windows
diff: @@ -725,9 +725,13 @@ export async function scanForClangCLKits(searchPaths: string[]): Promise<Promise
  }
  async function getVSInstallForKit(kit: Kit): Promise<VSInstallation|undefined> {
  - if (process.platform === "win32") {
  + if (process.platform !== "win32") {
  + return undefined;
  + }
  +
  console.assert(kit.visualStudio);
  console.assert(kit.visualStudioArchitecture);
  +
  const installs = await vsInstallations();
  const match = (inst: VSInstallation) =>
  // old Kit format
  @@ -739,7 +743,6 @@ async function getVSInstallForKit(kit: Kit): Promise<VSInstallation|undefined> {
  return installs.find(inst => match(inst));
  }
  -}
  export async function getVSKitEnvironment(kit: Kit): Promise<Map<string, string>|null> {
  const requested = await getVSInstallForKit(kit);
  