c++: Temporarily ignore -Wformat* warnings in dump_data_member_spec

The body of this function has been moved from eval_display_string_of,
which ignored some warnings already.
The new function doesn't ignore those, we we get
../../gcc/cp/reflect.cc: In function ‘void dump_data_member_spec(pretty_printer*, tree)’:
../../gcc/cp/reflect.cc:3692:18: warning: ‘T’ conversion used unquoted [-Wformat=]
 3692 |   pp_printf (pp, "(%T, %E, %E, %E, %s, {", TREE_VEC_ELT (r, 0),
      |                  ^~~~~~~~~~~~~~~~~~~~~~~~
../../gcc/cp/reflect.cc:3692:18: warning: spurious trailing punctuation sequence ‘{’ in format [-Wformat-diag]
../../gcc/cp/reflect.cc:3692:18: warning: unbalanced punctuation character ‘{’ in format [-Wformat-diag]
../../gcc/cp/reflect.cc:3699:18: warning: unbalanced punctuation character ‘}’ in format [-Wformat-diag]
 3699 |   pp_printf (pp, "})");
      |                  ^~~~
../../gcc/cp/reflect.cc:3699:18: warning: unbalanced punctuation character ‘)’ in format [-Wformat-diag]
extra warnings which can break bootstrap when promoted into errors.

2026-04-16  Jakub Jelinek  <jakub@redhat.com>

	* reflect.cc (dump_data_member_spec): Temporarily ignore
	-Wformat and -Wformat-diag warnings.