Fix some signed/unsigned comparison warnings.
Fix some signed/unsigned comparison warnings.

Patch by Hugh Bellamy
Differential Revision: https://reviews.llvm.org/D30926

git-svn-id: 4c4cc70b1ef44ba2b7963015e681894188cea27e@298099 91177308-0d34-0410-b5e6-96231b3b80d8

apple/swift-lldb,apple/swift-lldb,apple/swift-lldb,apple/swift-lldb,apple/swift-lldb,apple/swift-lldb