../../third_party/libxml/src/threads.c:876:14: error: comparison of function 'pthread_equal' not equal to a null pointer is always true [-Werror,-Wtautological-pointer-compare]
            (pthread_equal != NULL) &&
             ^~~~~~~~~~~~~    ~~~~
../../third_party/libxml/src/threads.c:876:14: note: prefix with the address-of operator to silence this warning
            (pthread_equal != NULL) &&
             ^
             &

../../third_party/libxml/src/debugXML.c:2939:11: error: comparison of array 'arg' equal to a null pointer is always false [-Werror,-Wtautological-pointer-compare]
            if ((arg == NULL) || (arg[0] == 0))
                 ^~~    ~~~~

The patch below fixes the warnings for me:


Index: libxml/src/threads.c
===================================================================
--- libxml/threads.c    (revision 256151)
+++ libxml/threads.c    (working copy)
@@ -873,7 +873,7 @@
             (pthread_cond_init != NULL) &&
             (pthread_cond_destroy != NULL) &&
             (pthread_cond_wait != NULL) &&
-            (pthread_equal != NULL) &&
+            (&pthread_equal != NULL) &&
             (pthread_self != NULL) &&
             (pthread_cond_signal != NULL)) {
             libxml_is_threaded = 1;

Index: third_party/libxml/src/debugXML.c
===================================================================
--- libxml/debugXML.c   (revision 256151)
+++ libxml/debugXML.c   (working copy)
@@ -2936,7 +2936,7 @@
         } else if (!strcmp(command, "save")) {
             xmlShellSave(ctxt, arg, NULL, NULL);
         } else if (!strcmp(command, "write")) {
-           if ((arg == NULL) || (arg[0] == 0)) 
+           if (arg[0] == 0)
                xmlGenericError(xmlGenericErrorContext,
                         "Write command requires a filename argument\n");
            else