[gcc r12-6285] c++: Add testcase for recently fixed PR [PR69681]

[Patrick Palka]

https://gcc.gnu.org/g:2793af17db239429ea3a2e26834e74daa6cff2c0

commit r12-6285-g2793af17db239429ea3a2e26834e74daa6cff2c0
Author: Patrick Palka <ppalka@redhat.com>
Date:   Thu Jan 6 10:42:50 2022 -0500

    c++: Add testcase for recently fixed PR [PR69681]
    
    Fixed ever since r12-6188.
    
            PR c++/69681
    
    gcc/testsuite/ChangeLog:
    
            * g++.dg/cpp0x/constexpr-compare2.C: New test.

Diff:
---
 gcc/testsuite/g++.dg/cpp0x/constexpr-compare2.C | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/gcc/testsuite/g++.dg/cpp0x/constexpr-compare2.C b/gcc/testsuite/g++.dg/cpp0x/constexpr-compare2.C
new file mode 100644
index 00000000000..b1bc4720805
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/constexpr-compare2.C
@@ -0,0 +1,10 @@
+// PR c++/69681
+// { dg-do compile { target c++11 } }
+
+void f();
+void g();
+static_assert(f != g, "");
+
+#if __cpp_constexpr >= 201603L
+static_assert([]{} != []{}, "");
+#endif