This implements WG14 N2927 and WG14 N2930, which together define the feature for typeof and typeof_unqual, which get the type of their argument as either fully qualified or fully unqualified. The argument to either operator is either a type name or an expression. If given a type name, the type information is pulled directly from the given name. If given an expression, the type information is pulled from the expression. Recursive use of these operators is allowed and has the expected behavior (the innermost operator is resolved to a type, and that's used to resolve the next layer of typeof specifier, until a fully resolved type is determined.
Note, we already supported typeof in GNU mode as a non-conforming extension and we are *not* exposing typeof_unqual as a non-conforming extension in that mode, nor are we exposing typeof or typeof_unqual as a nonconforming extension in other language modes. The GNU variant of typeof supports a form where the parentheses are elided from the operator when given an expression (e.g., typeof 0 i = 12;). When in C2x mode, we do not support this extension.