Remove weak symbol redefinitions when building on linux with gcc.

Causes a problem with fnl/musl due to #define of pthread_equal.
I think these aren't needed.

R=jamesr@chromium.org

Review URL: https://codereview.chromium.org/1402353007 .

third_party/libxml/src/threads.c

diff --git a/third_party/libxml/src/threads.c b/third_party/libxml/src/threads.c
index 98fd2c2..cc67548 100644
--- a/third_party/libxml/src/threads.c
+++ b/third_party/libxml/src/threads.c
@@ -47,49 +47,7 @@
 #ifdef HAVE_PTHREAD_H
 
 static int libxml_is_threaded = -1;
-#ifdef __GNUC__
-#ifdef linux
-#if (__GNUC__ == 3 && __GNUC_MINOR__ >= 3) || (__GNUC__ > 3)
-extern int pthread_once (pthread_once_t *__once_control,
-                         void (*__init_routine) (void))
-	   __attribute((weak));
-extern void *pthread_getspecific (pthread_key_t __key)
-	   __attribute((weak));
-extern int pthread_setspecific (pthread_key_t __key,
-                                __const void *__pointer)
-	   __attribute((weak));
-extern int pthread_key_create (pthread_key_t *__key,
-                               void (*__destr_function) (void *))
-	   __attribute((weak));
-extern int pthread_key_delete (pthread_key_t __key)
-	   __attribute((weak));
-extern int pthread_mutex_init ()
-	   __attribute((weak));
-extern int pthread_mutex_destroy ()
-	   __attribute((weak));
-extern int pthread_mutex_lock ()
-	   __attribute((weak));
-extern int pthread_mutex_unlock ()
-	   __attribute((weak));
-extern int pthread_cond_init ()
-	   __attribute((weak));
-extern int pthread_cond_destroy ()
-	   __attribute((weak));
-extern int pthread_cond_wait ()
-	   __attribute((weak));
-extern int pthread_equal ()
-	   __attribute((weak));
-extern pthread_t pthread_self ()
-	   __attribute((weak));
-extern int pthread_key_create ()
-	   __attribute((weak));
-extern int pthread_key_delete ()
-	   __attribute((weak));
-extern int pthread_cond_signal ()
-	   __attribute((weak));
-#endif
-#endif /* linux */
-#endif /* __GNUC__ */
+
 #endif /* HAVE_PTHREAD_H */
 
 /*