c++: noexcept and pointer to member function type [PR113108]

We ICE in nothrow_spec_p because it got a DEFERRED_NOEXCEPT.
This DEFERRED_NOEXCEPT was created in implicitly_declare_fn
when declaring

  Foo& operator=(Foo&&) = default;

in the test.  The problem is that in resolve_overloaded_unification
we call maybe_instantiate_noexcept before try_one_overload only in
the TEMPLATE_ID_EXPR case.

	PR c++/113108

gcc/cp/ChangeLog:

	* pt.cc (resolve_overloaded_unification): Call
	maybe_instantiate_noexcept.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp1z/noexcept-type28.C: New test.

(cherry picked from commit c755c7a)

Author: mpolacek

gcc/cp/pt.cc

@@ -23799,6 +23799,8 @@ resolve_overloaded_unification (tree tparms,
     for (lkp_iterator iter (arg); iter; ++iter)
       {
 	tree fn = *iter;
+	if (flag_noexcept_type)
+	  maybe_instantiate_noexcept (fn, tf_none);
 	if (try_one_overload (tparms, targs, tempargs, parm, TREE_TYPE (fn),
 			      strict, sub_strict, addr_p, explain_p)
 	    && (!goodfn || !decls_match (goodfn, fn)))

gcc/testsuite/g++.dg/cpp1z/noexcept-type28.C

@@ -0,0 +1,18 @@
+// PR c++/113108
+// { dg-do compile { target c++17 } }
+
+template <typename T>
+struct Foo {
+    Foo& operator=(Foo&&) = default;
+    T data;
+};
+
+template <typename T>
+void consume(Foo<T>& (Foo<T>::*)(Foo<T>&&) ) {}
+
+template <typename T>
+void consume(Foo<T>& (Foo<T>::*)(Foo<T>&&) noexcept) {}
+
+int main() {
+    consume(&Foo<int>::operator=);
+}