Tweak extension build for Leopard compatibility (wikitext, 7a51010)

These tweaks fix the build breakage under Leopard caused by the fact that the ANTLR runtime is non-Universal and Ruby is Universal. We set the ARCHFLAGS environment variable to force a non-Universal extension to be built.

In the future may actually produce a Universal version of the runtime, at which point will remove this somewhat kludgy hack.

Signed-off-by: Greg Hurrell <greg@hurrell.net>