+#if USE_WEAK_SYMBOLS
+#if defined(__GNUC__)
+# if defined __USE_ISOC99
+# define _cat_pragma(exp) _Pragma(#exp)
+# define _weak_pragma(exp) _cat_pragma(weak name)
+# else
+# define _weak_pragma(exp)
+# endif
+# define _declare(name) __extension__ extern __typeof__(name) name
+# define weak_symbol(name) _weak_pragma(name) _declare(name) __attribute__((weak))
+#endif
+#endif
+
+#ifdef USE_PTHREADS
+# if USE_WEAK_SYMBOLS
+weak_symbol(pthread_sigmask);
+weak_symbol(pthread_self);
+weak_symbol(pthread_equal);
+weak_symbol(pthread_mutex_init);
+weak_symbol(pthread_mutex_lock);
+weak_symbol(pthread_mutex_unlock);
+weak_symbol(pthread_mutex_trylock);
+weak_symbol(pthread_mutexattr_settype);
+weak_symbol(pthread_mutexattr_init);
+extern NCURSES_EXPORT(int) _nc_sigprocmask(int, const sigset_t *, sigset_t *);
+# undef sigprocmask
+# define sigprocmask _nc_sigprocmask
+# endif
+#endif
+