Add a little heuristic to Value::isUsedInBasicBlock to speed it up for small basic...

Add a little heuristic to Value::isUsedInBasicBlock to speed it up for small basic blocks.

- Calling getUser in a loop is much more expensive than iterating over a few instructions.
- Use it instead of the open-coded loop in AddrModeMatcher.
- 5% speedup on ARMDisassembler.cpp Release builds.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@145810 91177308-0d34-0410-b5e6-96231b3b80d8