[gcc r14-3456] libstdc++: Fix -Wunused-but-set-variable in std::format_to test

[Jonathan Wakely]

https://gcc.gnu.org/g:d6271d600d5a181b37093c8984990806a743f16a

commit r14-3456-gd6271d600d5a181b37093c8984990806a743f16a
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Thu Aug 24 11:42:17 2023 +0100

    libstdc++: Fix -Wunused-but-set-variable in std::format_to test
    
    libstdc++-v3/ChangeLog:
    
            * testsuite/std/format/functions/format_to.cc: Avoid warning for
            unused variables.

Diff:
---
 libstdc++-v3/testsuite/std/format/functions/format_to.cc | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/libstdc++-v3/testsuite/std/format/functions/format_to.cc b/libstdc++-v3/testsuite/std/format/functions/format_to.cc
index a35568954e2c..c5c3c503625c 100644
--- a/libstdc++-v3/testsuite/std/format/functions/format_to.cc
+++ b/libstdc++-v3/testsuite/std/format/functions/format_to.cc
@@ -69,14 +69,14 @@ test_move_only()
 {
   std::string str;
   move_only_iterator mo(std::back_inserter(str));
-  auto res = std::format_to(std::move(mo), "for{:.3} that{:c}",
-				     "matte", (int)'!');
+  [[maybe_unused]] auto res
+    = std::format_to(std::move(mo), "for{:.3} that{:c}", "matte", (int)'!');
   VERIFY( str == "format that!" );
 
   std::vector<wchar_t> vec;
   move_only_iterator wmo(std::back_inserter(vec));
-  auto wres = std::format_to(std::move(wmo), L"for{:.3} hat{:c}",
-				       L"matte", (long)L'!');
+  [[maybe_unused]] auto wres
+    = std::format_to(std::move(wmo), L"for{:.3} hat{:c}", L"matte", (long)L'!');
   VERIFY( std::wstring_view(vec.data(), vec.size()) == L"format hat!" );
 }