[libcxx] [test] Use TEST_IGNORE_NODISCARD.

Fixes D45595.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@329979 91177308-0d34-0410-b5e6-96231b3b80d8

test/std/localization/locales/locale.convenience/conversions/conversions.string/ctor_err_string.pass.cpp

@@ -33,7 +33,7 @@ int main()
         Myconv myconv;
         try
         {
-            (void)myconv.to_bytes(L"\xDA83");
+            TEST_IGNORE_NODISCARD myconv.to_bytes(L"\xDA83");
             assert(false);
         }
         catch (const std::range_error&)
@@ -41,7 +41,7 @@ int main()
         }
         try
         {
-            (void)myconv.from_bytes('\xA5');
+            TEST_IGNORE_NODISCARD myconv.from_bytes('\xA5');
             assert(false);
         }
         catch (const std::range_error&)
@@ -56,7 +56,7 @@ int main()
 #ifndef TEST_HAS_NO_EXCEPTIONS
         try
         {
-            (void)myconv.from_bytes('\xA5');
+            TEST_IGNORE_NODISCARD myconv.from_bytes('\xA5');
             assert(false);
         }
         catch (const std::range_error&)