[gcc(refs/vendors/ARM/heads/arm-struct-reorg-wip)] c++: Add testcase for PR 90764.

[Tamar Christina]

https://gcc.gnu.org/g:4d5bb56b1d3e6873a7d08dc8f5f4a4997e51bfde

commit 4d5bb56b1d3e6873a7d08dc8f5f4a4997e51bfde
Author: Jason Merrill <jason@redhat.com>
Date:   Sat Feb 15 14:48:08 2020 +0100

    c++: Add testcase for PR 90764.
    
         PR c++/90764
         * g++.dg/cpp1z/class-deduction69.C: New.

Diff:
---
 gcc/testsuite/g++.dg/cpp1z/class-deduction69.C | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/gcc/testsuite/g++.dg/cpp1z/class-deduction69.C b/gcc/testsuite/g++.dg/cpp1z/class-deduction69.C
new file mode 100644
index 00000000000..8291f4a649f
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1z/class-deduction69.C
@@ -0,0 +1,12 @@
+// PR c++/90764
+// { dg-do compile { target c++17 } }
+
+namespace a {
+  struct b;
+  template <typename...> using c = b;
+}
+template <typename... d> struct e : a::c<d...> { // { dg-error "incomplete" }
+  using a::c<>::c;		// { dg-prune-output "not a base" }
+};
+template <template <typename> typename f> void g() { f(); }
+void h() { g<e>(); }