Default +universal variant for configure-based ports

[Paul Guyot]

Dear all,

I've just implemented and committed a default +universal variant for  
configure-based ports. There's been some heat about +universal  
recently and I did not want every port to define the same code over  
and over.

This variant is more or less equivalent to:
variant universal {
	configure.args-append "--disable-dependency-tracking"
	configure.env-append CFLAGS="-isysroot /Developer/SDKs/ 
MacOSX10.4u.sdk -arch i386 -arch ppc" LDFLAGS="-arch i386 -arch ppc"
}

However, there is some additional magic:
* selecting the variant will fail if the port doesn't invoke  
configure (because user may think they can build the port universal  
while it would be effectless)
* selecting the variant will print a warning message if the port  
already overrides LDFLAGS or CFLAGS in the environment for the  
configure command
* you can add -O -g if the port requires it with just:
configure.universal_cflags-append	-O -g
* you can simply redefine the variant to override the default code  
and provide port-specific handler for the universal variant.

etc.

The variant is documented in portfile(7). I tested it with several  
ports and it seems to just work®™.

I'm considering some future enhancements, but let's see what it gives  
if we start building ports with +universal. Of course, the build will  
probably fail if dependencies were not built universal.

Enjoy!

Paul