test runner: Unix systems now put inferior dotest in its own process group.
test runner: Unix systems now put inferior dotest in its own process group.

This increases isolation as it relates to signal handling between parent and
children.


git-svn-id: 4c4cc70b1ef44ba2b7963015e681894188cea27e@248282 91177308-0d34-0410-b5e6-96231b3b80d8

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