[gcc r16-8460] libstdc++: Define foo() in optional/ref/access.cc test.

[Tomasz Kaminski]

https://gcc.gnu.org/g:b0cf247799072ee46c3fa13b43529c505f378068

commit r16-8460-gb0cf247799072ee46c3fa13b43529c505f378068
Author: Tomasz Kamiński <tkaminsk@redhat.com>
Date:   Sat Apr 4 10:33:36 2026 +0200

    libstdc++: Define foo() in optional/ref/access.cc test.
    
    Fix undefined reference error when compiling with -O0.
    
    libstdc++-v3/ChangeLog:
    
            * testsuite/20_util/optional/ref/access.cc: Provide
            definition for foo().

Diff:
---
 libstdc++-v3/testsuite/20_util/optional/ref/access.cc | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/libstdc++-v3/testsuite/20_util/optional/ref/access.cc b/libstdc++-v3/testsuite/20_util/optional/ref/access.cc
index 37c8ff355a66..dcd16a24b3c0 100644
--- a/libstdc++-v3/testsuite/20_util/optional/ref/access.cc
+++ b/libstdc++-v3/testsuite/20_util/optional/ref/access.cc
@@ -100,7 +100,7 @@ static_assert(  has_value_or_for<int(*)()> );
 int i;
 NonMovable nm;
 int arr[2];
-int foo();
+int foo() { return 1; }
 
 int main()
 {