Delay reads from !Machine.config before it is properly initialized.
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.