[libcxx] [test] Fix nodiscard warnings.

MSVC's STL has marked to_bytes/from_bytes as nodiscard.

Fixes D45595.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@329975 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/test/std/localization/locales/locale.convenience/conversions/conversions.string/ctor_err_string.pass.cpp b/test/std/localization/locales/locale.convenience/conversions/conversions.string/ctor_err_string.pass.cpp
index 70204c2..8126531 100644
--- a/test/std/localization/locales/locale.convenience/conversions/conversions.string/ctor_err_string.pass.cpp
+++ b/test/std/localization/locales/locale.convenience/conversions/conversions.string/ctor_err_string.pass.cpp
@@ -33,7 +33,7 @@
         Myconv myconv;
         try
         {
-            myconv.to_bytes(L"\xDA83");
+            (void)myconv.to_bytes(L"\xDA83");
             assert(false);
         }
         catch (const std::range_error&)
@@ -41,7 +41,7 @@
         }
         try
         {
-            myconv.from_bytes('\xA5');
+            (void)myconv.from_bytes('\xA5');
             assert(false);
         }
         catch (const std::range_error&)
@@ -56,7 +56,7 @@
 #ifndef TEST_HAS_NO_EXCEPTIONS
         try
         {
-            myconv.from_bytes('\xA5');
+            (void)myconv.from_bytes('\xA5');
             assert(false);
         }
         catch (const std::range_error&)