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

lldb/source/Target/Platform.cpp

@@ -527,12 +527,10 @@ RecurseCopy_Callback (void *baton,
         case FileSpec::eFileTypeInvalid:
         case FileSpec::eFileTypeOther:
         case FileSpec::eFileTypeUnknown:
+        default:
             rc_baton->error.SetErrorStringWithFormat("invalid file detected during copy: %s", src.GetPath().c_str());
             return FileSpec::eEnumerateDirectoryResultQuit; // got an error, bail out
             break;
-        default:
-            return FileSpec::eEnumerateDirectoryResultQuit; // unsupported file type, bail out
-            break;
     }
 }
 
@@ -1189,6 +1187,27 @@ Platform::CalculateMD5 (const FileSpec& file_spec,
         return false;
 }
 
+Error
+Platform::LaunchNativeProcess (
+    ProcessLaunchInfo &launch_info,
+    lldb_private::NativeProcessProtocol::NativeDelegate &native_delegate,
+    NativeProcessProtocolSP &process_sp)
+{
+    // Platforms should override this implementation if they want to
+    // support lldb-gdbserver.
+    return Error("unimplemented");
+}
+
+Error
+Platform::AttachNativeProcess (lldb::pid_t pid,
+                               lldb_private::NativeProcessProtocol::NativeDelegate &native_delegate,
+                               NativeProcessProtocolSP &process_sp)
+{
+    // Platforms should override this implementation if they want to
+    // support lldb-gdbserver.
+    return Error("unimplemented");
+}
+
 void
 Platform::SetLocalCacheDirectory (const char* local)
 {