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
diff --git a/config.h.in b/config.h.in
index debcbf8..fcc58bc 100644
--- a/config.h.in
+++ b/config.h.in
@@ -216,6 +216,9 @@
 /* The number of bytes in a time_t. */
 #undef SIZEOF_TIME_T
 
+/* The number of bytes in a pthread_t. */
+#undef SIZEOF_PTHREAD_T
+
 /* Defined to enable large file support when an off_t is bigger than a long
    and long long is available and at least as big as an off_t. You may need
    to add some flags for configuration and compilation to enable this mode.