message: not send a default standard
diff: @@ -22,13 +22,12 @@ const localize: nls.LocalizeFunc = nls.loadMessageBundle();
  const log = createLogger('cpptools');
  type Architecture = 'x86' | 'x64' | 'arm' | 'arm64' | undefined;
  -type StandardVersion = "c89" | "c99" | "c11" | "c17" | "c++98" | "c++03" | "c++11" | "c++14" | "c++17" | "c++20"
  - | "gnu89" | "gnu99" | "gnu11" | "gnu17" | "gnu++98" | "gnu++03" | "gnu++11" | "gnu++14" | "gnu++17" | "gnu++20";
  +type StandardVersion = "c89" | "c99" | "c11" | "c17" | "c++98" | "c++03" | "c++11" | "c++14" | "c++17" | "c++20" | "gnu89" | "gnu99" | "gnu11" | "gnu17" | "gnu++98" | "gnu++03" | "gnu++11" | "gnu++14" | "gnu++17" | "gnu++20";
  export interface CompileFlagInformation {
  extraDefinitions: string[];
  - standard: StandardVersion;
  + standard: StandardVersion | undefined;
  targetArch: Architecture;
  }
  @@ -41,7 +40,7 @@ interface TargetDefaults {
  defines: string[];
  }
  -function parseCppStandard(std: string, can_use_gnu: boolean): StandardVersion|null {
  +function parseCppStandard(std: string, can_use_gnu: boolean): StandardVersion | undefined {
  const is_gnu = can_use_gnu && std.startsWith('gnu');
  if (std.endsWith('++2a') || std.endsWith('++20') || std.endsWith('++latest')) {
  return is_gnu ? 'gnu++20' : 'c++20';
  @@ -56,11 +55,11 @@ function parseCppStandard(std: string, can_use_gnu: boolean): StandardVersion|nu
  } else if (std.endsWith('++98')) {
  return is_gnu ? 'gnu++98' : 'c++98';
  } else {
  - return null;
  + return undefined;
  }
  }
  -function parseCStandard(std: string, can_use_gnu: boolean): StandardVersion|null {
  +function parseCStandard(std: string, can_use_gnu: boolean): StandardVersion | undefined {
  // GNU options from: https://gcc.gnu.org/onlinedocs/gcc/C-Dialect-Options.html#C-Dialect-Options
  const is_gnu = can_use_gnu && std.startsWith('gnu');
  if (/(c|gnu)(90|89|iso9899:(1990|199409))/.test(std)) {
  @@ -77,7 +76,7 @@ function parseCStandard(std: string, can_use_gnu: boolean): StandardVersion|null
  return 'c11';
  }
  } else {
  - return null;
  + return undefined;
  }
  }
  @@ -117,7 +116,7 @@ export function parseCompileFlags(cptVersion: cpt.Version, args: string[], lang?
  const can_use_gnu_std = (cptVersion >= cpt.Version.v4);
  const iter = args[Symbol.iterator]();
  const extraDefinitions: string[] = [];
  - let standard: StandardVersion = (lang === 'C') ? 'c11' : 'c++17';
  + let standard: StandardVersion | undefined = undefined;
  let targetArch: Architecture = undefined;
  while (1) {
  const {done, value} = iter.next();
  