Fixtype of implementation environments.
This is a product type introduced by fty::defprod.
The following invariant is enforced on the fields:
(char+short+int+long+llong-format-wfp char+short+int+long+llong-format)
For now this only contains a few components, but we plan to add more components.
Currently we include the format of the three character types, and the standard signed integer types and their unsigned counterparts.
The reason for using the ``intermediate'' fixtype char+short+int+long+llong-format is the same as explained in integer-format about the ``intermediate'' fixtype used there. We may eliminate this at some point.