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/README b/README
index 57205d9..988ba90 100644
--- a/README
+++ b/README
@@ -307,6 +307,14 @@
         and type NMAKE.  Threading and sockets are supported by default
         in the resulting binaries of PYTHON15.DLL and PYTHON.EXE.
 
+Monterey (64-bit AIX):
+    The current Monterey C compiler (Visual Age) uses the OBJECT_MODE={32|64}
+    environment variable to set the compilation mode to either 32-bit or
+    64-bit (32-bit mode is the default). Presumably you want 64-bit
+    compilation mode for this 64-bit OS. As a result you must first set
+    OBJECT_MODE=64 in you environment before configuring (./configure) or
+    building (make) Python on Monterey.
+
 
 Configuring threads
 -------------------