[LDist][LVer] Explicitly pass the set of memchecks to LoopVersioning, NFC

Before the patch, the checks were generated internally in
addRuntimeCheck.  Now, we use the new overloaded version of
addRuntimeCheck that takes the ready-made set of checks as a parameter.

The checks are now generated by the client (LoopDistribution) with the
new RuntimePointerChecking::generateChecks API.

Also the new printChecks API is used to print out the checks for
debugging.

This is to continue the transition over to the new model whereby clients
will get the full set of checks from LAA, filter it and then pass it to
LoopVersioning and in turn to addRuntimeCheck.

llvm-svn: 243382