diagnostics: fix corrupt json/SARIF on stderr [PR114348]

diagnostics: fix corrupt json/SARIF on stderr [PR114348]

Various values of -fdiagnostics-format= request machine-readable output
on stderr, using JSON, but in various places we use fnotice to write
free-form text to stderr, such as "compilation terminated", leading to
corrupt JSON.

Fix by having fnotice skip the output for such cases.

gcc/ChangeLog:
	PR middle-end/114348
	* diagnostic-format-json.cc
	(json_stderr_output_format::machine_readable_stderr_p): New.
	(json_file_output_format::machine_readable_stderr_p): New.
	* diagnostic-format-sarif.cc
	(sarif_stream_output_format::machine_readable_stderr_p): New.
	(sarif_file_output_format::machine_readable_stderr_p): New.
	* diagnostic.cc (diagnostic_context::action_after_output): Move
	"fnotice" to before "finish" call, so that we still have the
	diagnostic_context.
	(fnotice): Bail out if the user requested one of the
	machine-readable diagnostic output formats on stderr.
	* diagnostic.h
	(diagnostic_output_format::machine_readable_stderr_p): New pure
	virtual function.
	(diagnostic_text_output_format::machine_readable_stderr_p): New.
	(diagnostic_context::get_output_format): New accessor.

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