Fix up TestLldbGdbServer C++ test slug exe.

Missing header for Linux, replaces with iostreams.


git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@208794 91177308-0d34-0410-b5e6-96231b3b80d8
Merge in upstream llvm.org 208794 into dev-tfiala-native-protocol-linux-x86_64
Enabled now-passing commandline attach process id check test.