c++: static lambda in template [PR108526]

c++: static lambda in template [PR108526]

tsubst_lambda_expr uses build_memfn_type to build a METHOD_TYPE for the new
lamba op().  This is not what we want for a C++23 static op(), but since we
also use that METHOD_TYPE to communicate the closure type down to
tsubst_function_decl, let's wait and turn it back at that point.

	PR c++/108526

gcc/cp/ChangeLog:

	* pt.cc (tsubst_function_decl): Handle static lambda.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp23/static-operator-call5.C: New test.