Use std::list::splice in TaskPool to avoid an allocation
Use std::list::splice in TaskPool to avoid an allocation

Using std::list::splice to move an element from one list to an other
avoids the allocation of a new element and a move of the data.

git-svn-id: 4c4cc70b1ef44ba2b7963015e681894188cea27e@251993 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