libstdc++: Add missing _GLIBCXX_USE_WCHAR_T checks in testsuite

These tests fail for a --disable-wchar_t build.

libstdc++-v3/ChangeLog:

	* testsuite/22_locale/conversions/buffer/1.cc: Check
	_GLIBCXX_USE_WCHAR_T.
	* testsuite/22_locale/conversions/buffer/3.cc: Likewise. Add
	test using char16_t.
	* testsuite/22_locale/conversions/string/1.cc: Check
	_GLIBCXX_USE_WCHAR_T.
	* testsuite/27_io/filesystem/path/generic/generic_string.cc:
	Likewise.
	* testsuite/27_io/filesystem/path/modifiers/make_preferred.cc:
	Likewise.
	* testsuite/27_io/filesystem/path/native/alloc.cc: Likewise.
	* testsuite/27_io/filesystem/path/native/string-char8_t.cc:
	Likewise.
	* testsuite/27_io/filesystem/path/native/string.cc: Likewise.
	* testsuite/28_regex/algorithms/regex_match/extended/wstring_locale.cc:
	Likewise.
	* testsuite/experimental/filesystem/path/generic/generic_string.cc:
	Likewise.
	* testsuite/experimental/filesystem/path/native/alloc.cc:
	Likewise.
	* testsuite/experimental/filesystem/path/native/string-char8_t.cc:
	Likewise.
	* testsuite/experimental/filesystem/path/native/string.cc:
	Likewise.

3 files changed, 25 insertions, 5 deletions

diff --git a/libstdc++-v3/testsuite/22_locale/conversions/buffer/1.cc b/libstdc++-v3/testsuite/22_locale/conversions/buffer/1.cc
index 2d5c094..9db7fce 100644
--- a/libstdc++-v3/testsuite/22_locale/conversions/buffer/1.cc
+++ b/libstdc++-v3/testsuite/22_locale/conversions/buffer/1.cc
@@ -31,12 +31,11 @@ template<typename Elem>
 using buf_conv = std::wbuffer_convert<cvt<Elem>, Elem>;
 
 using std::string;
-using std::stringstream;
 using std::wstring;
-using std::wstringstream;
 
 void test01()
 {
+#ifdef _GLIBCXX_USE_WCHAR_T
   buf_conv<wchar_t> buf;
   std::stringbuf sbuf;
   VERIFY( buf.rdbuf() == nullptr );
@@ -46,6 +45,7 @@ void test01()
 
   __gnu_test::implicitly_default_constructible test;
   test.operator()<buf_conv<wchar_t>>(); // P0935R0
+#endif
 }
 
 void test02()
@@ -53,7 +53,7 @@ void test02()
   std::stringbuf sbuf;
   buf_conv<char> buf(&sbuf);  // noconv
 
-  stringstream ss;
+  std::stringstream ss;
   ss.std::ios::rdbuf(&buf);
   string input = "King for a day...";
   ss << input << std::flush;
@@ -63,15 +63,17 @@ void test02()
 
 void test03()
 {
+#ifdef _GLIBCXX_USE_WCHAR_T
   std::stringbuf sbuf;
   buf_conv<wchar_t> buf(&sbuf);
 
-  wstringstream ss;
+  std::wstringstream ss;
   ss.std::wios::rdbuf(&buf);
   wstring input = L"Fool for a lifetime";
   ss << input << std::flush;
   string output = sbuf.str();
   VERIFY( output == "Fool for a lifetime" );
+#endif
 }
 
 int main()
diff --git a/libstdc++-v3/testsuite/22_locale/conversions/buffer/3.cc b/libstdc++-v3/testsuite/22_locale/conversions/buffer/3.cc
index 94aa43b..3e1d90f 100644
--- a/libstdc++-v3/testsuite/22_locale/conversions/buffer/3.cc
+++ b/libstdc++-v3/testsuite/22_locale/conversions/buffer/3.cc
@@ -38,21 +38,37 @@ private:
   char c = 'a';
 };
 
-struct codecvt : std::codecvt<wchar_t, char, std::mbstate_t> { };
 
 void
 test01()
 {
+#ifdef _GLIBCXX_USE_WCHAR_T
+  struct codecvt : std::codecvt<wchar_t, char, std::mbstate_t> { };
   // https://gcc.gnu.org/ml/libstdc++/2017-11/msg00022.html
   streambuf sb;
   std::wbuffer_convert<codecvt> conv(&sb);
   VERIFY( sb.in_avail() == 0 );
   wchar_t c = conv.sgetc();
   VERIFY( c == L'a' );
+#endif
+}
+
+
+void
+test02()
+{
+  struct codecvt : std::codecvt<char16_t, char, std::mbstate_t> { };
+  // https://gcc.gnu.org/ml/libstdc++/2017-11/msg00022.html
+  streambuf sb;
+  std::wbuffer_convert<codecvt, char16_t> conv(&sb);
+  VERIFY( sb.in_avail() == 0 );
+  char16_t c = conv.sgetc();
+  VERIFY( c == u'a' );
 }
 
 int
 main()
 {
   test01();
+  test02();
 }
diff --git a/libstdc++-v3/testsuite/22_locale/conversions/string/1.cc b/libstdc++-v3/testsuite/22_locale/conversions/string/1.cc
index 0016910..b5132da 100644
--- a/libstdc++-v3/testsuite/22_locale/conversions/string/1.cc
+++ b/libstdc++-v3/testsuite/22_locale/conversions/string/1.cc
@@ -51,6 +51,7 @@ void test01()
 
 void test02()
 {
+#ifdef _GLIBCXX_USE_WCHAR_T
   typedef str_conv<wchar_t> wsc;
   wsc c;
   string input = "Fool for a lifetime";
@@ -71,6 +72,7 @@ void test02()
 
   __gnu_test::implicitly_default_constructible test;
   test.operator()<wsc>(); // P0935R0
+#endif
 }
 
 int main()