pthread: Add enough so that coreutils/src/sort.c compiles.

pthread: Add enough so that coreutils/src/sort.c compiles.

* lib/pthread.in.h: Add self to author comment.  Conditionalize on
_GL_PTHREAD_H, not PTHREAD_H_, for consistency with the rest of
gnulib. Include <sched.h> and <time.h>, as per POSIX.
Include <sys/types.h>, in case it defines pthread_t.
(pthread_t, pthread_attr_t, pthread_barrier_t, pthread_barrierattr_t):
(pthread_cond_t, pthread_condattr_t, pthread_key_t, pthread_mutex_t):
(pthread_mutexattr_t, pthread_once_t, pthread_rwlock_t):
(pthread_rwlockattr_t, pthread_spinlock_t):
New typedefs, if HAVE_PTHREAD_T is not defined.
(PTHREAD_COND_INITIALIZER, PTHREAD_MUTEX_INITIALIZER):
(PTHREAD_ONCE_INIT, PTHREAD_RWLOCK_INITIALIZER):
(PTHREAD_BARRIER_SERIAL_THREAD, PTHREAD_CANCEL_DEFERRED):
(PTHREAD_CANCEL_ASYNCHRONOUS, PTHREAD_CANCEL_ENABLE):
(PTHREAD_CANCEL_DISABLE, PTHREAD_CANCELED, PTHREAD_CREATE_JOINABLE):
(PTHREAD_CREATE_DETACHED, PTHREAD_INHERIT_SCHED):
(PTHREAD_EXPLICIT_SCHED, PTHREAD_MUTEX_DEFAULT, PTHREAD_MUTEX_NORMAL):
(PTHREAD_MUTEX_ERRORCHECK, PTHREAD_MUTEX_RECURSIVE):
(PTHREAD_MUTEX_STALLED, PTHREAD_MUTEX_ROBUST, PTHREAD_PRIO_NONE):
(PTHREAD_PRIO_INHERIT, PTHREAD_PRIO_PROTECT, PTHREAD_PROCESS_PRIVATE):
(PTHREAD_PROCESS_SHARED, PTHREAD_SCOPE_SYSTEM, PTHREAD_SCOPE_PROCESS):
New macros.
(pthread_cond_destroy, pthread_cond_init, pthread_cond_signal):
(pthread_cond_wait, pthread_exit, pthread_mutex_destroy):
(pthread_mutex_init, pthread_mutex_lock, pthread_mutex_unlock):
(pthread_spin_init, pthread_spin_lock, pthread_spin_trylock);
(pthread_spin_unlock): New dummy functions.
(pthread_create): Return EAGAIN; don't set errno.
* m4/pthread.m4 (gl_PTHREAD_CHECK): Check for pthread_t, and
require AC_C_INLINE.
* modules/pthread (Depends-on): Add sched, time.
(pthread.h): Use AM_V_GEN.