c++: replace tf_norm with a local flag

c++: replace tf_norm with a local flag

The tf_norm flag controlling whether to build diagnostic information
during constraint normalization doesn't need to be a global tsubst flag,
and is confusingly named.  This patch replaces it with a boolean flag
local to normalization.

gcc/cp/ChangeLog:

	* constraint.cc (norm_info::norm_info): Take a bool instead of
	tsubst_flags_t.
	(norm_info::generate_diagnostics): Turn this predicate function
	into a bool data member.
	(normalize_logical_operation): Adjust after norm_info changes.
	(normalize_concept_check): Likewise.
	(normalize_atom): Likewise.
	(get_normalized_constraints_from_info): Likewise.
	(normalize_concept_definition): Likewise.
	(normalize_constraint_expression): Likewise.
	(normalize_placeholder_type_constraints): Likewise.
	(satisfy_nondeclaration_constraints): Likewise.
	* cp-tree.h (enum tsubst_flags): Remove tf_norm.

Reviewed-by: Jason Merrill <jason@redhat.com>