[LAA] Begin moving the logic of generating checks out of addRuntimeCheck

Summary:
The goal is to start moving us closer to the model where
RuntimePointerChecking will compute and store the checks.  Then a client
can filter the check according to its requirements and then use the
filtered list of checks with addRuntimeCheck.

Before the patch, this is all done in addRuntimeCheck.  So the patch
starts to split up addRuntimeCheck while providing the old API under
what's more or less a wrapper now.

The new underlying addRuntimeCheck takes a collection of checks now,
expands the code for the bounds then generates the code for the checks.

I am not completely happy with making expandBounds static because now it
needs so many explicit arguments but I don't want to make the type
PointerBounds part of LAI.  This should get fixed when addRuntimeCheck
is moved to LoopVersioning where it really belongs, IMO.

Audited the assembly diff of the testsuite (including externals).  There
is a tiny bit of assembly churn that is due to the different order the
code for the bounds is expanded now
(MultiSource/Benchmarks/Prolangs-C/bison/conflicts.s and with LoopDist
on 456.hmmer/fast_algorithms.s).

Reviewers: hfinkel

Subscribers: klimek, llvm-commits

Differential Revision: http://reviews.llvm.org/D11205

llvm-svn: 243239