[PassManager] Ensure destructors of cached AnalysisUsage objects are run

In 254760, I introduced the usage of a BumpPtrAllocator for the AnalysisUsage instances held by the PassManger.  This turns out to have been incorrect since a BumpPtrAllocator does not run the destructors of objects when deallocating memory.  Since a few of our SmallVector's had grown beyond their small size, we end up with some leaked memory.  We need to use a SpecificBumpPtrAllocator instead.

llvm-svn: 254803