Add lldb-gdbserver support for Linux x86_64.

This change brings in lldb-gdbserver (llgs) specifically for Linux x86_64.
(More architectures coming soon).

Not every debugserver option is covered yet.  Currently
the lldb-gdbserver command line can start unattached,
start attached to a pid (process-name attach not supported yet),
or accept lldb attaching and launching a process or connecting
by process id.

The history of this large change can be found here:
https://github.com/tfiala/lldb/tree/dev-tfiala-native-protocol-linux-x86_64

Until mid/late April, I was not sharing the work and continued
to rebase it off of head (developed via id tfiala@google.com).  I switched over to
user todd.fiala@gmail.com in the middle, and once I went to github, I did
merges rather than rebasing so I could share with others.

llvm-svn: 212069
diff --git a/lldb/source/Plugins/DynamicLoader/POSIX-DYLD/AuxVector.cpp b/lldb/source/Plugins/DynamicLoader/POSIX-DYLD/AuxVector.cpp
index c079d0f..04a6792 100644
--- a/lldb/source/Plugins/DynamicLoader/POSIX-DYLD/AuxVector.cpp
+++ b/lldb/source/Plugins/DynamicLoader/POSIX-DYLD/AuxVector.cpp
@@ -57,11 +57,10 @@
 DataBufferSP
 AuxVector::GetAuxvData()
 {
-#if defined(__linux__) || defined(__FreeBSD__)
-    if (m_process->GetPluginName() == ProcessElfCore::GetPluginNameStatic())
-        return static_cast<ProcessElfCore *>(m_process)->GetAuxvData();
-#endif
-    return lldb_private::Host::GetAuxvData(m_process);
+    if (m_process)
+        return m_process->GetAuxvData ();
+    else
+        return DataBufferSP ();
 }
 
 void