set deployment target from macports.conf

[Anders F Björklund]

Ryan Schmidt wrote:

>> Theoretically +universal should be able to handle this,
>> but cross-compiling isn't really supported in MacPorts.
>
> Yeah. So why did we expose the options in macports.conf again? :)

Note that macports.conf in trunk has some more features...
(which still isn't "supported", but rather "experimental")

universal_target	10.4
universal_sysroot	/Developer/SDKs/MacOSX10.4u.sdk
universal_archs		ppc i386

That has a somewhat better chance of making the right
thing than hacking macosx_deployment_target or flags.

--anders