Fixing warnings shouldn't introduce a crasher.
Fixing warnings shouldn't introduce a crasher.

Fix the warning the correct way without making things crash when ENABLE_MUTEX_ERROR_CHECKING is non enabled.

<rdar://problem/17703039>


git-svn-id: 4c4cc70b1ef44ba2b7963015e681894188cea27e@213394 91177308-0d34-0410-b5e6-96231b3b80d8

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