Add diagnostic_metadata and CWE support

This patch adds support for associating a diagnostic message with an
optional diagnostic_metadata object, so that plugins can add extra data
to their diagnostics (e.g. mapping a diagnostic to a taxonomy or coding
standard such as from CERT or MISRA).

Currently this only supports associating a CWE identifier with a
diagnostic (which is what I'm using for the warnings in the analyzer
patch kit), but adding a diagnostic_metadata class allows for future
growth in this area without an explosion of further "warning_at"
overloads for all of the different kinds of custom data that a plugin
might want to add.

This version of the patch renames the overly-general
-fdiagnostics-show-metadata to -fdiagnostics-show-cwe and adds test
coverage for it via a plugin.

It also adds a note to the documentation that no GCC diagnostics
currently use this; it's a feature for plugins (and, at some point,
I hope, the analyzer).

gcc/ChangeLog:
	* common.opt (fdiagnostics-show-cwe): Add.
	* diagnostic-core.h (class diagnostic_metadata): New forward decl.
	(warning_at): Add overload taking a const diagnostic_metadata &.
	(emit_diagnostic_valist): Add overload taking a
	const diagnostic_metadata *.
	* diagnostic-format-json.cc: Include "diagnostic-metadata.h".
	(json_from_metadata): New function.
	(json_end_diagnostic): Call it to add "metadata" child for
	diagnostics with metadata.
	(diagnostic_output_format_init): Clear context->show_cwe.
	* diagnostic-metadata.h: New file.
	* diagnostic.c: Include "diagnostic-metadata.h".
	(diagnostic_impl): Add const diagnostic_metadata * param.
	(diagnostic_n_impl): Likewise.
	(diagnostic_initialize): Initialize context->show_cwe.
	(diagnostic_set_info_translated): Initialize diagnostic->metadata.
	(get_cwe_url): New function.
	(print_any_cwe): New function.
	(diagnostic_report_diagnostic): Call print_any_cwe if the
	diagnostic has non-NULL metadata.
	(emit_diagnostic): Pass NULL as the metadata in the call to
	diagnostic_impl.
	(emit_diagnostic_valist): Likewise.
	(emit_diagnostic_valist): New overload taking a
	const diagnostic_metadata *.
	(inform): Pass NULL as the metadata in the call to
	diagnostic_impl.
	(inform_n): Likewise for diagnostic_n_impl.
	(warning): Likewise.
	(warning_at): Likewise.  Add overload that takes a
	const diagnostic_metadata &.
	(warning_n): Pass NULL as the metadata in the call to
	diagnostic_n_impl.
	(pedwarn): Likewise for diagnostic_impl.
	(permerror): Likewise.
	(error): Likewise.
	(error_n): Likewise.
	(error_at): Likewise.
	(sorry): Likewise.
	(sorry_at): Likewise.
	(fatal_error): Likewise.
	(internal_error): Likewise.
	(internal_error_no_backtrace): Likewise.
	* diagnostic.h (diagnostic_info::metadata): New field.
	(diagnostic_context::show_cwe): New field.
	* doc/invoke.texi (-fno-diagnostics-show-cwe): New option.
	* opts.c (common_handle_option): Handle OPT_fdiagnostics_show_cwe.
	* toplev.c (general_init): Initialize global_dc->show_cwe.

gcc/testsuite/ChangeLog:
	* gcc.dg/plugin/diagnostic-test-metadata.c: New test.
	* gcc.dg/plugin/diagnostic_plugin_test_metadata.c: New test plugin.
	* gcc.dg/plugin/plugin.exp (plugin_test_list): Add them.

From-SVN: r279556