Fix the -Wunused-function warning properly (MachProcess.mm)
Fix the -Wunused-function warning properly (MachProcess.mm)

r319938 was not NFC, because it got the preprocessor guard wrong. Check
WITH_FBS and WITH_BKS before defining SplitEventData.

git-svn-id: 4c4cc70b1ef44ba2b7963015e681894188cea27e@319943 91177308-0d34-0410-b5e6-96231b3b80d8

apple/swift-lldb,apple/swift-lldb,apple/swift-lldb,apple/swift-lldb,apple/swift-lldb,llvm-mirror/lldb,llvm-mirror/lldb,llvm-mirror/lldb,apple/swift-lldb,llvm-mirror/lldb,llvm-mirror/lldb