Unfortunately, the decision to decide which library to link must be made
before (or during) the first call made to any one of the library functions.
Since MPI_THREAD_INIT can't be called until after MPI_INIT is called,
MPI_THREAD_INIT may not be able to decide which library to load.
1. MPI_THREAD_INIT is called in place of MPI_INIT, not after MPI_INIT.
2. The current proposal does not prevent a static specification of the
level of thread support required at link time. It is just that such
specification is implementation dependent.