IR: Avoid mallocs in constructor of ModuleSlotTracker

A ModuleSlotTracker can be created without actually being used (e.g.,
r266889 added one to the Verifier).  Create the SlotTracker within it
lazily on the first call to ModuleSlotTracker::getMachine.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@266902 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed