MacOS X: Enable 4-way universal builds

This patch adds a new configure argument on OSX:
        --with-universal-archs=[32-bit|64-bit|all]

When used with the --enable-universalsdk option this controls which
CPU architectures are includes in the framework. The default is 32-bit,
meaning i386 and ppc. The most useful alternative is 'all', which includes
all 4 CPU architectures supported by MacOS X (i386, ppc, x86_64 and ppc64).

This includes limited support for the Carbon bindings in 64-bit mode as well,
limited because (a) I haven't done extensive testing and (b) a large portion
of the Carbon API's aren't available in 64-bit mode anyway.

I've also duplicated a feature of Apple's build of python: setting the
environment variable 'ARCHFLAGS' controls the '-arch' flags used for building
extensions using distutils.

Lib/distutils/util.py

@@ -125,12 +125,19 @@ def get_platform ():
             osname = "macosx"
 
 
-            if (release + '.') < '10.4.' and \
-                    get_config_vars().get('UNIVERSALSDK', '').strip():
+            if (release + '.') >= '10.4.' and \
+                    '-arch' in get_config_vars().get('CFLAGS', '').strip():
                 # The universal build will build fat binaries, but not on
                 # systems before 10.4
+                #
+                # Try to detect 4-way universal builds, those have machine-type
+                # 'universal' instead of 'fat'.
+
                 machine = 'fat'
 
+                if '-arch x86_64' in get_config_vars().get('CFLAGS'):
+                    machine = 'universal'
+
             elif machine in ('PowerPC', 'Power_Macintosh'):
                 # Pick a sane name for the PPC architecture.
                 machine = 'ppc'