[PATCH] libstdc++: Fix recent flat_map test with COW string

[Patrick Palka]

Tested on x86_64-pc-linux-gnu with 
--target_board=unix/-D_GLIBCXX_USE_CXX11_ABI=0
OK for trunk and 16?

-- >8 --

libstdc++-v3/ChangeLog:

        * testsuite/23_containers/flat_map/1.cc (test_constexpr):
        If std::string isn't constexpr don't run test10.
---
 libstdc++-v3/testsuite/23_containers/flat_map/1.cc | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/libstdc++-v3/testsuite/23_containers/flat_map/1.cc 
b/libstdc++-v3/testsuite/23_containers/flat_map/1.cc
index 096b9eeac3e4..1cb088f511eb 100644
--- a/libstdc++-v3/testsuite/23_containers/flat_map/1.cc
+++ b/libstdc++-v3/testsuite/23_containers/flat_map/1.cc
@@ -330,7 +330,9 @@ test_constexpr()
   test07();
   test08();
   test09();
+#if __cpp_lib_constexpr_string >= 201907L
   test10();
+#endif
   return true;
 }
 
-- 
2.54.0.rc1.54.g60f07c4f5c