Define LIBXML2_DEFINED in the Xcode project for Xcode builds so Darwin builds can take advantage of the new GDB register info from the target XML.

Also add "#if defined( LIBXML2_DEFINED )" around code that already used libxml2 in SymbolVendorMacOSX.cpp.

Cleaned up some warnings in ProcessGDBRemote.cpp.

llvm-svn: 235144
diff --git a/lldb/source/Plugins/Process/gdb-remote/ProcessGDBRemote.cpp b/lldb/source/Plugins/Process/gdb-remote/ProcessGDBRemote.cpp
index 6f36310..dc61ec8 100644
--- a/lldb/source/Plugins/Process/gdb-remote/ProcessGDBRemote.cpp
+++ b/lldb/source/Plugins/Process/gdb-remote/ProcessGDBRemote.cpp
@@ -3491,7 +3491,7 @@
     { "data_ptr", GdbServerRegisterInfo::eDataPtr  },
     { "code_ptr", GdbServerRegisterInfo::eCodePtr  },
     { "i387_ext", GdbServerRegisterInfo::eI387Ext  }, // 80bit fpu
-    { nullptr } // sentinel
+    { nullptr   , GdbServerRegisterInfo::eUnknown  }  // sentinel
 };
 
 // find the first sibling with a matching name