Add -fdiagnostics-format={json-stderr|json-file}

Add -fdiagnostics-format={json-stderr|json-file}

This commit adds -fdiagnostics-format=json-file, writing to
DUMP_BASE_NAME.gcc.json, and adds -fdiagnostics-format=json-stderr,
a synonym for the existing -fdiagnostics-format=json.

gcc/ChangeLog:
	* common.opt (fdiagnostics-format=): Add json-stderr and json-file
	to description.
	(DIAGNOSTICS_OUTPUT_FORMAT_JSON): Rename to...
	(DIAGNOSTICS_OUTPUT_FORMAT_JSON_STDERR): ...this.
	(diagnostics_output_format): Add json-stderr and json-file.
	* diagnostic-format-json.cc (json_flush_to_file): New.
	(json_final_cb): Convert to...
	(json_flush_to_file): ...this, ...
	(json_stderr_final_cb): ...this, and...
	(json_file_final_cb): ...this.
	(diagnostic_output_format_init): Move to diagnostic.cc.
	(json_output_base_file_name): New.
	(diagnostic_output_format_init_json): New.
	(diagnostic_output_format_init_json_stderr): New.
	(diagnostic_output_format_init_json_file): New.
	* diagnostic.cc (diagnostic_output_format_init): Move here from
	diagnostic-format-json.cc; update for changes to enum.
	* diagnostic.h (enum diagnostics_output_format): Rename
	DIAGNOSTICS_OUTPUT_FORMAT_JSON to
	DIAGNOSTICS_OUTPUT_FORMAT_JSON_STDERR, and add
	DIAGNOSTICS_OUTPUT_FORMAT_JSON_FILE.
	(diagnostic_output_format_init): Add base_file_name param.
	(diagnostic_output_format_init_json_stderr): New decl.
	(diagnostic_output_format_init_json_file): New dec.
	* doc/invoke.texi (-fdiagnostics-format=): Add "json-stderr" and
	"json-file".  Rewrite so that the existing "json" is a synonym of
	"json-stderr".
	* gcc.cc (driver_handle_option): Pass dump_base_name to
	diagnostic_output_format_init.
	* opts.cc (common_handle_option): Likewise.

gcc/testsuite/ChangeLog:
	* c-c++-common/diagnostic-format-json-file-1.c: New test.
	* c-c++-common/diagnostic-format-json-stderr-1.c: New test.

Signed-off-by: David Malcolm <dmalcolm@redhat.com>