TailDuplication: Extract Indirect-Branch block limit as option. NFC

The existing code hard-coded a limit of 20 instructions for duplication
when a block ended with an indirect branch. Extract this as an option.
No functional change intended.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@280125 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed