Initial implementation of PIC16 Cloner pass.

Initial implementation of PIC16 Cloner pass.

This pass is supposed to be run on the linked .bc module.
It traveses the module call graph twice. Once starting from the main function
and marking each reached function as "ML". Again, starting from the ISR
and cloning any reachable function that was marked as "ML". After cloning
the function, it remaps all the call sites in IL functions to call the
cloned functions.

Currently only marking is being done.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@96435 91177308-0d34-0410-b5e6-96231b3b80d8