Mark `constexpr` symbols as macros and use direct replacement
(non-function symbols) or in-place evaluation (uses of `constexpr`
function symbols).

Attach the "ellipsis" information to the declarator and not to the type.

This reverts commit 4c299cc716f9e0bf639411296f1ee5f2c5d96300.

Now follows the grammar described in the C++ standard: Explicit type
conversions are postfix expressions. This required adding rules for C++
cast expressions, which in turn simplifies type checking for we no
longer treat them as function calls with template arguments.