Move __PTHREAD_SPINS definition to architecture specific header

This patch moves the __PTHREAD_SPINS definition to arch specific header
since pthread_mutex_t layout is also arch specific.  This leads to no
need to defining __PTHREAD_MUTEX_HAVE_ELISION and thus removing of the
undefined compiler warning.

sysdeps/unix/sysv/linux/alpha/nptl/bits/pthreadtypes.h

@@ -73,6 +73,9 @@ typedef union
   long int __align;
 } pthread_mutex_t;
 
+/* Mutex __spins initializer used by PTHREAD_MUTEX_INITIALIZER.  */
+#define __PTHREAD_SPINS 0
+
 typedef union
 {
   char __size[__SIZEOF_PTHREAD_MUTEXATTR_T];