Add "rust-enabled" to --version output

This adds "rust-enabled" to the --version output, so it's easier to
tell if lldb has rust support.

Author: tromey

lldb/source/Version/Version.cpp

@@ -67,6 +67,8 @@ const char *lldb_private::GetVersion() {
       g_version_str += "\n  llvm revision ";
       g_version_str += llvm_rev;
     }
+
+    g_version_str += "\n  rust-enabled";
   }
 
   return g_version_str.c_str();