This patch implements a -fdiagnostics-format=json option which
converts the diagnostics to be output to stderr in a JSON format;
see the documentation in invoke.texi.

Logically-related diagnostics are nested at the JSON level, using
the auto_diagnostic_group mechanism.

gcc/ChangeLog:
	PR other/19165
	* Makefile.in (OBJS): Move json.o to...
	(OBJS-libcommon): ...here and add diagnostic-format-json.o.
	* common.opt (fdiagnostics-format=): New option.
	(diagnostics_output_format): New enum.
	* diagnostic-format-json.cc: New file.
	* diagnostic.c (default_diagnostic_final_cb): New function, taken
	from start of diagnostic_finish.
	(diagnostic_initialize): Initialize final_cb to
	default_diagnostic_final_cb.
	(diagnostic_finish): Move "being treated as errors" messages to
	default_diagnostic_final_cb.  Call any final_cb.
	(default_diagnostic_finalizer): Add diagnostic_t param.
	(diagnostic_report_diagnostic): Pass "orig_diag_kind" to
	diagnostic_finalizer callback.
	* diagnostic.h (enum diagnostics_output_format): New enum.
	(diagnostic_finalizer_fn): Reimplement, adding diagnostic_t param.
	(struct diagnostic_context): Add "final_cb".
	(default_diagnostic_finalizer): Add diagnostic_t param.
	(diagnostic_output_format_init): New decl.
	* doc/invoke.texi (-fdiagnostics-format): New option.
	* dwarf2out.c (gen_producer_string): Ignore
	OPT_fdiagnostics_format_.
	* gcc.c (driver_handle_option): Handle OPT_fdiagnostics_format_.
	* lto-wrapper.c (append_diag_options): Ignore it.
	* opts.c (common_handle_option): Handle it.

gcc/c-family/ChangeLog:
	PR other/19165
	* c-opts.c (c_diagnostic_finalizer): Add diagnostic_t param.

gcc/fortran/ChangeLog:
	PR other/19165
	* error.c (gfc_diagnostic_finalizer): Add diagnostic_t param.

gcc/jit/ChangeLog:
	PR other/19165
	* dummy-frontend.c (jit_begin_diagnostic): Add diagnostic_t param.

gcc/testsuite/ChangeLog:
	PR other/19165
	* c-c++-common/diagnostic-format-json-1.c: New test.
	* c-c++-common/diagnostic-format-json-2.c: New test.
	* c-c++-common/diagnostic-format-json-3.c: New test.
	* c-c++-common/diagnostic-format-json-4.c: New test.
	* c-c++-common/diagnostic-format-json-5.c: New test.
	* gcc.dg/plugin/diagnostic_plugin_test_show_locus.c
	(custom_diagnostic_finalizer): Add diagnostic_t param.
	* gcc.dg/plugin/location_overflow_plugin.c
	(verify_unpacked_ranges): Likewise.
	(verify_no_columns): Likewise.
	* gfortran.dg/diagnostic-format-json-1.F90: New test.
	* gfortran.dg/diagnostic-format-json-2.F90: New test.
	* gfortran.dg/diagnostic-format-json-3.F90: New test.

From-SVN: r266186