[EarlyCSE] Change C API pass interface for EarlyCSE w/ MemorySSA

Previous change broke the C API for creating an EarlyCSE pass w/
MemorySSA by adding a bool parameter to control whether MemorySSA was
used or not.  This broke the OCaml bindings.  Instead, change the old C
API entry point back and add a new one to request an EarlyCSE pass with
MemorySSA.

llvm-svn: 280379