[gcc r15-4666] libstdc++: Disable parts of new test that depend on constexpr std::string

[Jonathan Wakely]

https://gcc.gnu.org/g:a4931587cbccdb6aff352f9df728ab468c5260b9

commit r15-4666-ga4931587cbccdb6aff352f9df728ab468c5260b9
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Thu Oct 24 20:12:08 2024 +0100

    libstdc++: Disable parts of new test that depend on constexpr std::string
    
    The compile-time assertions don't work with -D_GLIBCXX_USE_CXX11_ABI=0.
    
    libstdc++-v3/ChangeLog:
    
            * testsuite/21_strings/basic_string/operators/char/op_plus_string_view.cc:
            Check __cpp_lib_constexpr_string.

Diff:
---
 .../21_strings/basic_string/operators/char/op_plus_string_view.cc       | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/libstdc++-v3/testsuite/21_strings/basic_string/operators/char/op_plus_string_view.cc b/libstdc++-v3/testsuite/21_strings/basic_string/operators/char/op_plus_string_view.cc
index 364d5bd5abab..2d474519f60a 100644
--- a/libstdc++-v3/testsuite/21_strings/basic_string/operators/char/op_plus_string_view.cc
+++ b/libstdc++-v3/testsuite/21_strings/basic_string/operators/char/op_plus_string_view.cc
@@ -44,6 +44,7 @@ struct convertible_to_lots
   constexpr operator std::string() const { return "convertible_to_lots3"; }
 };
 
+#if __cpp_lib_constexpr_string >= 201907 // constexpr std::string
 using namespace std::literals;
 static_assert( "costa "s + "marbella"sv == "costa marbella"s );
 static_assert( "costa "sv + "marbella"s == "costa marbella"s );
@@ -52,6 +53,7 @@ static_assert( "costa "s + convertible_to_string_view2{} == "costa convertible_t
 static_assert( "costa "s + convertible_to_string_view3{} == "costa convertible_to_sv3 non_const"s );
 static_assert( "costa "s + convertible_to_string_view_and_char_star{} == "costa convertible_to_sv_and_charstar1"s );
 static_assert( "costa "s + convertible_to_lots{} == "costa convertible_to_lots1"s );
+#endif // __cpp_lib_constexpr_string
 
 void
 test01()