[gcc r11-8097] c++: Add testcase for already fixed PR [PR90215]

[Patrick Palka <ppalka@gcc.gnu.org>]

https://gcc.gnu.org/g:00c3c31be43c018870569a599200a8af84956487

commit r11-8097-g00c3c31be43c018870569a599200a8af84956487
Author: Patrick Palka <ppalka@redhat.com>
Date:   Fri Apr 9 11:37:42 2021 -0400

    c++: Add testcase for already fixed PR [PR90215]
    
    We accept this testcase after r11-7985.
    
    gcc/testsuite/ChangeLog:
    
            PR c++/90215
            * g++.dg/cpp1z/fold-lambda4.C: New test.

Diff:
---
 gcc/testsuite/g++.dg/cpp1z/fold-lambda4.C | 30 ++++++++++++++++++++++++++++++
 1 file changed, 30 insertions(+)

diff --git a/gcc/testsuite/g++.dg/cpp1z/fold-lambda4.C b/gcc/testsuite/g++.dg/cpp1z/fold-lambda4.C
new file mode 100644
index 00000000000..b8bae8602ad
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1z/fold-lambda4.C
@@ -0,0 +1,30 @@
+// PR c++/90215
+// { dg-do compile { target c++17 } }
+
+struct X
+{
+    template <class F>
+    void f(F f)
+    {
+        f(0);
+    }
+};
+
+template <class... Xs>
+void bug(Xs... xs)
+{
+    int i;
+
+    [&](auto&... ys)
+    {
+        (xs.f([&](auto)
+        {
+            ys;
+        }), ...);
+    }(i);
+}
+
+int main()
+{
+    bug(X{});
+}