Remove the state_types array.

If we want to add support for making std::cin and std::cout optional, it
is impractical to have all of the mbstate_t objects in one array. This
would mean that if std::cin and std::cout are omitted, the state_types
array is only used partially.

Solve this by using separate global variables. These are placed right
next to the iostream object and the buffer, meaning we can easily #ifdef
them away.

Differential Revision:	http://reviews.llvm.org/D8359

llvm-svn: 233274