Change SymbolVendor::GetCompileUnitAtIndex() and SymbolVendor::Dump() to make sure they are thread safe. 
Change SymbolVendor::GetCompileUnitAtIndex() and SymbolVendor::Dump() to make sure they are thread safe. 

<rdar://problem/20263111>


git-svn-id: 4c4cc70b1ef44ba2b7963015e681894188cea27e@234951 91177308-0d34-0410-b5e6-96231b3b80d8

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