diagnostics: introduce class diagnostic_option_classifier

diagnostics: introduce class diagnostic_option_classifier

This patch gathers the 6 fields in diagnostic_context relating to
keeping track of overriding the severity of warnings, and
pushing/popping those severities, moving them all into a new class
diagnostic_option_classifier.

No functional change intended.

gcc/ChangeLog:
	* diagnostic.cc (diagnostic_context::push_diagnostics): Convert
	to...
	(diagnostic_option_classifier::push): ...this.
	(diagnostic_context::pop_diagnostics): Convert to...
	(diagnostic_option_classifier::pop): ...this.
	(diagnostic_context::initialize): Move code to...
	(diagnostic_option_classifier::init): ...this new function.
	(diagnostic_context::finish): Move code to...
	(diagnostic_option_classifier::fini): ...this new function.
	(diagnostic_context::classify_diagnostic): Convert to...
	(diagnostic_option_classifier::classify_diagnostic): ...this.
	(diagnostic_context::update_effective_level_from_pragmas): Convert
	to...
	(diagnostic_option_classifier::update_effective_level_from_pragmas):
	...this.
	(diagnostic_context::diagnostic_enabled): Update for refactoring.
	* diagnostic.h (struct diagnostic_classification_change_t): Move into...
	(class diagnostic_option_classifier): ...this new class.
	(diagnostic_context::option_unspecified_p): Update for move of
	fields into m_option_classifier.
	(diagnostic_context::classify_diagnostic): Likewise.
	(diagnostic_context::push_diagnostics): Likewise.
	(diagnostic_context::pop_diagnostics): Likewise.
	(diagnostic_context::update_effective_level_from_pragmas): Delete.
	(diagnostic_context::m_classify_diagnostic): Move into class
	diagnostic_option_classifier.
	(diagnostic_context::m_option_classifier): Likewise.
	(diagnostic_context::m_classification_history): Likewise.
	(diagnostic_context::m_n_classification_history): Likewise.
	(diagnostic_context::m_push_list): Likewise.
	(diagnostic_context::m_n_push): Likewise.
	(diagnostic_context::m_option_classifier): New.

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