[gcc r11-6771] libstdc++: Only test writing to wostream if supported [PR 98725]

[Jonathan Wakely]

https://gcc.gnu.org/g:ec153f96f8943f1d2418d2248ed219358990bb5f

commit r11-6771-gec153f96f8943f1d2418d2248ed219358990bb5f
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Mon Jan 18 14:23:13 2021 +0000

    libstdc++: Only test writing to wostream if supported [PR 98725]
    
    libstdc++-v3/ChangeLog:
    
            PR libstdc++/98725
            * testsuite/20_util/unique_ptr/io/lwg2948.cc:  Do not try to
            write to a wide character stream if wide character support is
            disabled in the library.

Diff:
---
 libstdc++-v3/testsuite/20_util/unique_ptr/io/lwg2948.cc | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/libstdc++-v3/testsuite/20_util/unique_ptr/io/lwg2948.cc b/libstdc++-v3/testsuite/20_util/unique_ptr/io/lwg2948.cc
index ab0b17d2b1c..131bfb24ed7 100644
--- a/libstdc++-v3/testsuite/20_util/unique_ptr/io/lwg2948.cc
+++ b/libstdc++-v3/testsuite/20_util/unique_ptr/io/lwg2948.cc
@@ -73,8 +73,10 @@ template<typename D>
 
 static_assert( streamable<std::ostream, Unique_ptr<deleter<char>>> );
 static_assert( ! streamable<std::ostream, Unique_ptr<deleter<wchar_t>>> );
+#ifdef _GLIBCXX_USE_WCHAR_T
 static_assert( ! streamable<std::wostream, Unique_ptr<deleter<char>>> );
 static_assert( streamable<std::wostream, Unique_ptr<deleter<wchar_t>>> );
+#endif
 
 void
 test02()