Begin staging in support for TCGv_i128 with Int128.
Define the type enumerator, the typedef, and the
helper-head.h macros.
This cannot yet be used, because you can't allocate
temporaries of this new type.
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>