Several definitions in Cutil and elsewhere were accessing the default
value of !Machine.config, before it is properly initialized in Driver.
Delay evaluation of these definitions, and initialize Machine.config
to nonsensical values so that lack of initialization is caught early
(e.g. in Cutil.find_matching_*_kind).

Also, following up on commit [3b8a094d], don't use "wchar_t" typedef
to type wide string literals, even if this typedef is in scope.
The risk here is to hide an inconsistency between "wchar_t"'s definition
in standard headers and CompCert's built-in definition.