Don't refer to pthread_cancel in libgcc

gcc/gthr-posix.h

 /* Threads compatibility routines for libgcc2 and libobjc.  */
 /* Compile this one with gcc.  */
 /* Copyright (C) 1997, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007,
    2008, 2009 Free Software Foundation, Inc.
 
 This file is part of GCC.
 
 GCC is free software; you can redistribute it and/or modify it under
 the terms of the GNU General Public License as published by the Free
 Software Foundation; either version 3, or (at your option) any later
@@ skipping 33 matching lines @@
 typedef pthread_t __gthread_t;
 typedef pthread_key_t __gthread_key_t;
 typedef pthread_once_t __gthread_once_t;
 typedef pthread_mutex_t __gthread_mutex_t;
 typedef pthread_mutex_t __gthread_recursive_mutex_t;
 typedef pthread_cond_t __gthread_cond_t;
 typedef struct timespec __gthread_time_t;
 
 /* POSIX like conditional variables are supported.  Please look at comments
    in gthr.h for details. */
-#define __GTHREAD_HAS_COND      1       
+#define __GTHREAD_HAS_COND      1
 
 #define __GTHREAD_MUTEX_INIT PTHREAD_MUTEX_INITIALIZER
 #define __GTHREAD_ONCE_INIT PTHREAD_ONCE_INIT
 #if defined(PTHREAD_RECURSIVE_MUTEX_INITIALIZER)
 #define __GTHREAD_RECURSIVE_MUTEX_INIT PTHREAD_RECURSIVE_MUTEX_INITIALIZER
 #elif defined(PTHREAD_RECURSIVE_MUTEX_INITIALIZER_NP)
 #define __GTHREAD_RECURSIVE_MUTEX_INIT PTHREAD_RECURSIVE_MUTEX_INITIALIZER_NP
 #else
 #define __GTHREAD_RECURSIVE_MUTEX_INIT_FUNCTION __gthread_recursive_mutex_init_function
 #endif
@@ skipping 162 matching lines @@
         __gthread_active = 0;
 
       __gthread_active_latest_value = __gthread_active;
     }
 
   return __gthread_active_latest_value != 0;
 }
 
 #else /* neither FreeBSD nor Solaris */
 
+/* For a program to be multi-threaded the only thing that it certainly must
+   be using is pthread_create.  However, there may be other libraries that
+   intercept pthread_create with their own definitions to wrap pthreads
+   functionality for some purpose.  In those cases, pthread_create being
+   defined might not necessarily mean that libpthread is actually linked
+   in.
+
+   For the GNU C library, we can use a known internal name.  This is always
+   available in the ABI, but no other library would define it.  That is
+   ideal, since any public pthread function might be intercepted just as
+   pthread_create might be.  __pthread_key_create is an "internal"
+   implementation symbol, but it is part of the public exported ABI.  Also,
+   it's among the symbols that the static libpthread.a always links in
+   whenever pthread_create is used, so there is no danger of a false
+   negative result in any statically-linked, multi-threaded program.
+
+   For others, we choose pthread_cancel as a function that seems unlikely
+   to be redefined by an interceptor library.  The bionic (Android) C
+   library does not provide pthread_cancel, so we do use pthread_create
+   there (and interceptor libraries lose).  */
+
+#ifdef __GLIBC__
+__gthrw2(__gthrw_(__pthread_key_create),
+         __pthread_key_create,
+         pthread_key_create)
+# define GTHR_ACTIVE_PROXY      __gthrw_(__pthread_key_create)
+#elif defined (__BIONIC__)
+# define GTHR_ACTIVE_PROXY      __gthrw_(pthread_create)
+#else
+# define GTHR_ACTIVE_PROXY      __gthrw_(pthread_cancel)
+#endif
+
 static inline int
 __gthread_active_p (void)
 {
-  static void *const __gthread_active_ptr 
-    = __extension__ (void *) &__gthrw_(pthread_cancel);
+  static void *const __gthread_active_ptr
+    = __extension__ (void *) &GTHR_ACTIVE_PROXY;
   return __gthread_active_ptr != 0;
 }
 
 #endif /* FreeBSD or Solaris */
 
 #else /* not SUPPORTS_WEAK */
 
 /* Similar to Solaris, HP-UX 11 for PA-RISC provides stubs for pthread
    calls in shared flavors of the HP-UX C library.  Most of the stubs
    have no functionality.  The details are described in the "libc cumulative
@@ skipping 634 matching lines @@
 
 static inline int
 __gthread_cond_destroy (__gthread_cond_t* __cond)
 {
   return __gthrw_(pthread_cond_destroy) (__cond);
 }
 
 #endif /* _LIBOBJC */
 
 #endif /* ! GCC_GTHR_POSIX_H */