This patch partly (some stuff went in already) ports Python to Monterey.

- Fix bug in thread_pthread.h::PyThread_get_thread_ident() where
  sizeof(pthread) < sizeof(long).
- Add 'configure' for:
	- SIZEOF_PTHREAD is pthread_t can be included via <pthread.h>
	- setting Monterey system name
	- appropriate CC,LINKCC,LDSHARED,OPT, and CCSHARED for Monterey
- Add section in README for Monterey build

Python/thread_pthread.h

@@ -171,6 +171,13 @@ PyThread_start_new_thread(void (*func)(void *), void *arg)
 	return success != 0 ? 0 : 1;
 }
 
+/* XXX This implementation is considered (to quote Tim Peters) "inherently
+   hosed" because:
+     - It does not guanrantee the promise that a non-zero integer is returned.
+     - The cast to long is inherently unsafe.
+     - It is not clear that the 'volatile' (for AIX?) and ugly casting in the
+       latter return statement (for Alpha OSF/1) are any longer necessary.
+*/
 long 
 PyThread_get_thread_ident(void)
 {
@@ -179,7 +186,11 @@ PyThread_get_thread_ident(void)
 		PyThread_init_thread();
 	/* Jump through some hoops for Alpha OSF/1 */
 	threadid = pthread_self();
+#if SIZEOF_PTHREAD_T <= SIZEOF_LONG
+	return (long) threadid;
+#else
 	return (long) *(long *) &threadid;
+#endif
 }
 
 static void