diagnostic: Use vec instead of custom array reallocations for m_classification_histor...

diagnostic: Use vec instead of custom array reallocations for m_classification_history/m_push_list [PR116847]

diagnostic.h already relies on vec.h, it uses auto_vec in one spot.

The following patch converts m_classification_history and m_push_list
hand-managed arrays to vec templates.
The main advantage is exponential rather than linear reallocation,
e.g. with current libstdc++ headers if one includes all the standard
headers there could be ~ 300 reallocations of the m_classification_history
array (sure, not all of them will result in actually copying the data, but
still).
In addition to that it fixes some formatting issues in the code.

2024-09-26  Jakub Jelinek  <jakub@redhat.com>

	PR libstdc++/116847
	* diagnostic.h (diagnostic_option_classifier): Change type
	of m_classification_history from diagnostic_classification_change_t *
	to vec<diagnostic_classification_change_t>.  Change type of
	m_push_list from int * to vec<int>.  Remove m_n_classification_history
	and m_n_push members.
	* diagnostic.cc (diagnostic_option_classifier::init): Set m_push_list
	to vNULL rather than nullptr.  Don't initialize m_n_push.  Initialize
	m_classification_history to vNULL.
	(diagnostic_option_classifier::fini): Call release () method on
	m_push_list instead of free on it.  Call release () on
	m_classification_history.  Don't clear m_n_push.
	(diagnostic_option_classifier::push): Adjust for m_push_list and
	m_classification_history being vectors rather than custom allocated
	arrays with counter.
	(diagnostic_option_classifier::pop): Likewise.
	(classify_diagnostic): Adjust for m_classification_history being
	vector rather than custom allocated array with counter.
	(update_effective_level_from_pragmas): Likewise.