Fix a few warnings/errors for compiling with -fno-exceptions.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@178267 91177308-0d34-0410-b5e6-96231b3b80d8

src/locale.cpp

@@ -6003,6 +6003,8 @@ void __throw_runtime_error(const char* msg)
 {
 #ifndef _LIBCPP_NO_EXCEPTIONS
     throw runtime_error(msg);
+#else
+    (void)msg;
 #endif
 }