[BinaryStream] Defaultify copy and move constructors.

The various BinaryStream classes had explicit copy constructors
which resulted in deleted move constructors.  This was causing
the internal std::shared_ptr to get copied rather than moved
very frequently, since these classes are often used as return
values.

Patch by Alex Telishev
Differential Revision: https://reviews.llvm.org/D36942

llvm-svn: 311368