Gary found a compile time problem, fixes #78823 Daniel

* xpath.c: Gary found a compile time problem, fixes #78823
Daniel
diff --git a/xpath.c b/xpath.c
index da6d088..05ec0d2 100644
--- a/xpath.c
+++ b/xpath.c
@@ -392,7 +392,7 @@
 xmlXPathCompSwap(xmlXPathStepOpPtr op) {
     int tmp;
 
-#ifdef LIBXML_THREAD_ENABLED
+#ifndef LIBXML_THREAD_ENABLED
     /*
      * Since this manipulates possibly shared variables, this is
      * disable if one detects that the library is used in a multithreaded