c-family: add name_hint/deferred_diagnostic

c-family: add name_hint/deferred_diagnostic

In various places we use lookup_name_fuzzy to provide a hint,
and can report messages of the form:
  error: unknown foo named 'bar'
or:
  error: unknown foo named 'bar'; did you mean 'SUGGESTION?

This patch provides a way for lookup_name_fuzzy to provide
both the suggestion above, and (optionally) additional hints
that can be printed e.g.

  note: did you forget to include <SOME_HEADER.h>?

This patch provides the mechanism and ports existing users
of lookup_name_fuzzy to the new return type.
There are no uses of such hints in this patch, but followup
patches provide various front-end specific uses of this.

gcc/c-family/ChangeLog:
	* c-common.h (enum lookup_name_fuzzy_kind): Move to name-hint.h.
	(lookup_name_fuzzy): Likewise.  Convert return type from
	const char * to name_hint.  Add location_t param.
	* name-hint.h: New header.

gcc/c/ChangeLog:
	* c-decl.c: Define INCLUDE_UNIQUE_PTR before including system.h.
	Include "c-family/name-hint.h"
	(implicit_decl_warning): Convert "hint" from
	const char * to name_hint.  Pass location to
	lookup_name_fuzzy.  Suppress any deferred diagnostic if the
	warning was not printed.
	(undeclared_variable): Likewise for "guessed_id".
	(lookup_name_fuzzy): Convert return type from const char *
	to name_hint.  Add location_t param.
	* c-parser.c: Define INCLUDE_UNIQUE_PTR before including system.h.
	Include "c-family/name-hint.h"
	(c_parser_declaration_or_fndef): Convert "hint" from
	const char * to name_hint.  Pass location to lookup_name_fuzzy.
	(c_parser_parameter_declaration): Likewise.

gcc/cp/ChangeLog:
	* name-lookup.c: Define INCLUDE_UNIQUE_PTR before including system.h.
	Include "c-family/name-hint.h"
	(suggest_alternatives_for): Convert "fuzzy_name" from const char *
	to name_hint, and rename to "hint".  Pass location to
	lookup_name_fuzzy.
	(lookup_name_fuzzy): Convert return type from const char *
	to name_hint.  Add location_t param.
	* parser.c: Define INCLUDE_UNIQUE_PTR before including system.h.
	Include "c-family/name-hint.h"
	(cp_parser_diagnose_invalid_type_name): Convert
	"suggestion" from const char * to name_hint, and rename to "hint".
	Pass location to lookup_name_fuzzy.

From-SVN: r254963