How to force exactly one variant.

[Martin Krischik]

Hello,

I have a little problem gnat-gcc port: You need to specify a bootstrap
compiler - that is exactly one. Which leaves me with two problems:

1) if no bootstrap compiler is specified I would like to display a
helpful description.

2) If two bootstrap compiler are chosen then an error should be displayed

Any ideas from the Portfile gurus?

Martin
-- 
Martin Krischik
krischik at users.sourceforge.net