Remove C language front end dependencies.

Remove C language front end dependencies.
* tree-convert.c: New file.
* treetree.c: Don't include c-tree.h.  Include target.h.
(struct lang_identifier, union lang_tree_node, struct lang_type,
struct lang_function): New, minimal language-specific datastructs.
(tree_lang_truthvalue_conversion, tree_mark_addressable,
tree_lang_type_for_size, tree_lang_type_for_mode,
tree_lang_unsigned_type, tree_lang_signed_type,
tree_lang_signed_or_unsigned): New functions.
(LANG_HOOKS_*): Don't use C front end langhooks.  Use new functions.
(pushlevel, poplevel, global_bindings_p, insert_block, set_block,
pushdecl, getdecls, kept_level_p, tree_push_type_decl,
tree_push_atomic_type_decl): New functions.
(struct resword, struct reswords): Remove.
* Make-lang.in: Update.  Don't depend on C front end objects.
* config-lang.in: Likewise.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@69178 138bc75d-0d04-0410-961f-82ee72b054a4