c++: Missing SFINAE with lookup_fnfields [PR78446]

c++: Missing SFINAE with lookup_fnfields [PR78446]

Here we're failing to do SFINAE in build_op_call when looking up the
class's operator() via lookup_fnfields, which calls lookup_member always
with complain=tf_warning_or_error; from there we would complain
about an ambiguous lookup for operator().

This patch fixes this by adding a tsubst_flags_t parameter to
lookup_fnfields and adjusting all its callers appropriately.

gcc/cp/ChangeLog:

	PR c++/78446
	* call.c (build_op_call): Pass complain to lookup_fnfields.
	(build_special_member_call): Likewise.
	* class.c (type_requires_array_cookie): Pass tf_warning_or_error
	to lookup_fnfields.
	* cp-tree.h (lookup_fnfields): Add tsubst_flags_t parameter.
	* except.c (build_throw): Pass tf_warning_or_error to
	lookup_fnfields.
	* init.c (build_new_1): Pass complain to lookup_fnfields.
	* method.c (locate_fn_flags): Likewise.
	* name-lookup.c (lookup_name_real_1): Pass tf_warning_or_error
	to lookup_fnfields.
	* pt.c (tsubst_baselink): Pass complain to lookup_fnfields.
	* search.c (lookup_fnfields): New 'complain' parameter.  Pass it
	to lookup_member.

gcc/testsuite/ChangeLog:

	PR c++/78446
	* g++.dg/template/sfinae31.C: New test.