* c-decl.c (named_labels, shadowed_labels, label_level_chain)

	(push_label_level, pop_label_level): Kill.
	(struct binding_level): Rename level_chain to outer.
	Add outer_function field.  Change parm_flag, function_body,
	keep, keep_if_subblocks to 1-bit bitfields of type bool.
	(current_function_level): New variable.
	(keep_next_level_flag, keep_next_if_subblocks): Change type to bool.
	(keep_next_level, declare_parm_level, warn_if_shadowing):
	Update to match.
	(struct language_function): Kill named_labels, shadowed_labels fields.
	(c_init_decl_processing, start_function, c_push__function_context)
	(c_pop_function_context): No need to muck with named_labels nor
	shadowed_labels.

	(make_binding_level): No need to clear the structure here.
	(pop_binding_level): Always operate on current_binding_level.
	Update current_function_level if necessary.
	(pushlevel): Don't clear named_labels.  Update current_function_level
	if necessary.  Use "true" and "false" where appropriate.
	(poplevel): Diagnose labels defined but not used, or vice
	versa, and clear out label-meanings leaving scope, while
	walking down the decls list, for all binding levels.
	Handle LABEL_DECLs appearing in the shadowed list.
	pop_binding_level takes no arguments.
	(pushdecl_function_level): Use current_function_level.

	(make_label, bind_label): New static functions.
	(declare_label): New exported function.
	(lookup_label, define_label): Rewritten for new data structure.
	(shadow_label): Kill.

	* c-tree.h: Prototype declare_label; don't prototype
	push_label_level, pop_label_level, nor shadow_label.
	* c-parse.in: Remove all calls to push_label_level and
	pop_label_level.  Use declare_label for __label__ decls.

	* doc/extend.texi: Clarify that __label__ can be used to
	declare labels with local scope in any nested block, not
	just statement expressions.  Cross-reference nested functions
	section from local labels section.

testsuite:
	* gcc.dg/noncompile/label-1.c: New comprehensive test case for
	diagnostics of ill-formed constructs involving labels.
	* gcc.dg/noncompile/label-lineno-1.c: Add error regexp for
	the new 'previously defined here' message.

From-SVN: r69597