[PATCH] Allow _MSC_EXTENSIONS macro on non-Windows targets

[Yunzhong Gao]

  > They're not keywords, they're weird ways of spelling things like && and |.
  > Under MSVC compat mode, we should not recognize them at all (MSVC doesn't do
  > so in its default mode, and appears to treat them as macros in its
  > "conforming" mode).

  In that case, something like the following should return true if the operator
  token is to be recognized. Right?

  bool isSpecialOperatorToken(IdentifierInfo *II)
  {
    if (LangOpts.MSVCCompat)
      return false;
    return II->isCPlusPlusOperatorKeyword();
  }

  > You could instead provide an __is_identifier, which I think might be what
  > you're really looking for here ("is this token usable as an identifier?").

  True, but I would prefer if it is called something else.
  All the other __has_***() methods return true if the given parameter is
  something special, whereas it seems that __is_identifier() would return
  false if something is special (hence not an identifier).
  Maybe __has_special_token(parameter)?

http://llvm-reviews.chandlerc.com/D3034