c++: Add lang_decl, type_decl API

[Nathan Sidwell]

We need	to call	the lang_decl and type_decl creators from the module
loading machinery.  This makes them reachable.

         gcc/cp/
         * cp-tree.h (maybe_add_lang_decl_raw, maybe_add_lang_type_raw):
         Declare.
         * lex.c (maybe_add_lang_decl_raw, maybe_add_lang_type_raw):
         Externalize, reformat.

pushing to trunk

-- 
Nathan Sidwell
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