Use ThreadLauncher to launch TaskPool threads
Use ThreadLauncher to launch TaskPool threads

Summary:
This allows for the stack size to be configured, which isn't
possible with std::thread. Prevents overflowing the stack when
performing complex operations in the task pool on darwin,
where the default pthread stack size is only 512kb.

Reviewers: labath, tberghammer, clayborg

Subscribers: lldb-commits

Differential Revision: https://reviews.llvm.org/D37930

git-svn-id: 4c4cc70b1ef44ba2b7963015e681894188cea27e@313537 91177308-0d34-0410-b5e6-96231b3b80d8

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